Allow token to come from Kubernetes Secret rather than plaintext in Helm values

[pwhack]

Attempting to resolve #14.

Goals:

• When config.token is specified, maintain existing chart behavior.
• When config.token_secret_ref is specified, omit token from ConfigMap and modify Deployment to include an environment variable pulled from the Kubernetes Secret.
• Attempt to modify values.schema.json to require one of config.token or config.token_secret_ref but that they are mutually exclusive.

Testing procedure:

1. (PASSED) ConfigMap should not contain token_secret_ref but should contain token. Deployment should not contain token environment variable.

   helm template hd-agent \
     ./agent \
     --namespace datalake-fivetran \
     --set config.data_volume_pvc=fivetran-agent-pvc \
     --set config.token="token-value-here" \
   > testfile.yaml

2. (PASSED) ConfigMap should not contain token_secret_ref and should not contain token. Deployment should contain token environment variable populated by Secret.

   helm template hd-agent \
     ./agent \
     --namespace datalake-fivetran \
     --set config.data_volume_pvc=fivetran-agent-pvc \
     --set config.token_secret_ref="secret-name-here" \
   > testfile.yaml

STILL TO DO:

• Take a stab at updating values.schema.json. I've never used JSON Schema.

[pwhack]

I don't know how to modify the JSON Schema so that either config.token or config.token_secret_ref are required but mutually exclusive. Maybe someone else can resolve that.