feat(api-tokens): add optional api-tokens

[aaldebs99]

Summary

Attempt 2!

This PR aims to implement optional API tokens used to access the API when basic or OIDC auth is enabled.

Example configuration:

security:
  api:
    tokens:
      - "my-secret-token-123"
      - "${API_TOKEN_FROM_ENV}"
      - "my-secret-token-2

This allows you to provide one of those tokens to API calls with the Authorization header:

curl http://localhost:8080/api/v1/config
{"announcements":[],"authenticated":false,"oidc":false}⏎

curl http://localhost:8080/api/v1/config -H "Authorization: Bearer my-secret-token-123"
{"announcements":[],"authenticated":true,"oidc":false}⏎

curl http://localhost:8080/api/v1/config -H "Authorization: Bearer my-secret-token-2"
{"announcements":[],"authenticated":true,"oidc":false}

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Updated documentation in README.md, if applicable.