feat: ssh_tunnel (MeltanoLabs#156)

Adds the ability to forward through an ssh tunnel, copying logic from
https://github.com/MeltanoLabs/tap-postgres. Also removes unused snippet
from sinks.py. Includes an additional test to validate ssh_tunnel config
and respective docker additions.

Closes MeltanoLabs#145 
Closes MeltanoLabs#155

README.md

@@ -26,12 +26,20 @@ Built with the [Meltano SDK](https://sdk.meltano.com) for Singer Taps and Target
 | default_target_schema        | False    | None    | Postgres schema to send data to, example: tap-clickup |
 | hard_delete                  | False    |       0 | When activate version is sent from a tap this specefies if we should delete the records that don't match, or mark them with a date in the `_sdc_deleted_at` column. |
 | add_record_metadata          | False    |       1 | Note that this must be enabled for activate_version to work!This adds _sdc_extracted_at, _sdc_batched_at, and more to every table. See https://sdk.meltano.com/en/latest/implementation/record_metadata.html for more information. |
+| ssh_tunnel                   | False    | None    | SSH Tunnel Configuration, this is a json object |
+| ssh_tunnel.enable   | True (if ssh_tunnel set) | False   | Enable an ssh tunnel (also known as bastion host), see the other ssh_tunnel.* properties for more details.
+| ssh_tunnel.host | True (if ssh_tunnel set) | False   | Host of the bastion host, this is the host we'll connect to via ssh
+| ssh_tunnel.username | True (if ssh_tunnel set) | False   |Username to connect to bastion host
+| ssh_tunnel.port | True (if ssh_tunnel set) | 22 | Port to connect to bastion host
+| ssh_tunnel.private_key | True (if ssh_tunnel set) | None | Private Key for authentication to the bastion host
+| ssh_tunnel.private_key_password | False | None | Private Key Password, leave None if no password is set
 | ssl_enable                   | False    |       0 | Whether or not to use ssl to verify the server's identity. Use ssl_certificate_authority and ssl_mode for further customization. To use a client certificate to authenticate yourself to the server, use ssl_client_certificate_enable instead. Note if sqlalchemy_url is set this will be ignored. |
 | ssl_client_certificate_enable| False    |       0 | Whether or not to provide client-side certificates as a method of authentication to the server. Use ssl_client_certificate and ssl_client_private_key for further customization. To use SSL to verify the server's identity, use ssl_enable instead. Note if sqlalchemy_url is set this will be ignored. |
 | ssl_mode                     | False    | verify-full | SSL Protection method, see [postgres documentation](https://www.postgresql.org/docs/current/libpq-ssl.html#LIBPQ-SSL-PROTECTION) for more information. Must be one of disable, allow, prefer, require, verify-ca, or verify-full. Note if sqlalchemy_url is set this will be ignored. |
-| ssl_certificate_authority    | False    | None    | The certificate authority that should be used to verify the server's identity. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
-| ssl_client_certificate              | False    | None    | The certificate that should be used to verify your identity to the server. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
-| ssl_client_private_key              | False    | None    | The private key for the certificate you provided. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
+| ssl_certificate_authority    | False    | ~/.postgresql/root.crl | The certificate authority that should be used to verify the server's identity. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
+| ssl_client_certificate       | False    | ~/.postgresql/postgresql.crt | The certificate that should be used to verify your identity to the server. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
+| ssl_client_private_key       | False    | ~/.postgresql/postgresql.key | The private key for the certificate you provided. Can be provided either as the certificate itself (in .env) or as a filepath to the certificate. Note if sqlalchemy_url is set this will be ignored. |
+| ssl_storage_directory        | False    | .secrets | The folder in which to store SSL certificates provided as raw values. When a certificate/key is provided as a raw value instead of as a filepath, it must be written to a file before it can be used. This configuration option determines where that file is created. |
 | stream_maps                  | False    | None    | Config object for stream maps capability. For more information check out [Stream Maps](https://sdk.meltano.com/en/latest/stream_maps.html). |
 | stream_map_config            | False    | None    | User-defined config values to be used within map expressions. |
 | flattening_enabled           | False    | None    | 'True' to enable schema flattening and automatically expand nested properties. |

docker-compose.yml

@@ -25,3 +25,36 @@ services:
       POSTGRES_PASSWORD: postgres
     ports:
       - 5433:5432
+  ssh:
+    image: ghcr.io/linuxserver/openssh-server:9.1_p1-r2-ls106 # This docker repo has added breaking changes a lot in the last month, pinning this.
+    container_name: openssh-server
+    hostname: openssh-server
+    environment:
+      - PUID=1000
+      - PGID=1000
+      - PUBLIC_KEY_FILE=/config/ssh_host_keys/ssh_host_rsa_key.pub
+      - SUDO_ACCESS=false
+      - PASSWORD_ACCESS=false
+      - USER_NAME=melty
+    volumes:
+      - ./ssh_tunnel/ssh-server-config:/config/ssh_host_keys:ro
+    ports:
+      - "127.0.0.1:2223:2222"
+    networks:
+      - inner
+  postgresdb:
+    image: postgres:13.0
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: main
+    networks:
+      inner:
+        ipv4_address: 10.5.0.5
+networks:
+  inner:
+    driver: bridge
+    ipam:
+     config:
+       - subnet: 10.5.0.0/16
+         gateway: 10.5.0.1