[LLT-5563] Add TLS and domain names to core-api and mqtt

[olekoliinyk]

Problem

In context of esp32-meshnet nat-lab integration tests, device emulator is going to send requests to https://api.nordvpn.com. So far, nat-lab core-api was not supporting tls connection and core-api domain.

Solution

• Add self-signed certificate with CN=*.nordvpn.com" record. Certificate is used for core-api as well as for mqtt broker.
• Add core-api and mqtt broker DNS records
• Refractor core-api and notification center tests to use self-signed certificate when sending API requests to core-api
• Add core-api extra-hosts record to cone-client-01 in docker-compose.yml. This is only for core-api and notification center tests. esp32 emulator is going to use nat-lab DNS server to resolve requested domains.
• For test_notification_center.py self-singed certificate is not used for connection to mqtt broker due to the fact that test is executed on the host and there is no mqtt.nordvpn.com DNS records. In context of this test, it might be not so relevant as the purpose of the test is to verify mqtt messages. If there is any issue with tls connection to the mqtt-broker, it will be failing then either on docker compose level or core-api tests.

☑️ Definition of Done checklist

• Commit history is clean (requirements)
• README.md is updated
• Functionality is covered by unit or integration tests

[ThrasherLT]

lgtm, but I'm not an expert on python and https, so +0.5

[gytsto]

+1

[tomaszklak]

+1, nice :)