chore(health): add dedicated liveness and readiness endpoints

[iainsproat]

Description & motivation

When Redis fails, but Postgres is still responding, the existing liveness probe continues responding and indicating the server was healthy.

We need a more complex query to account for the state of Redis as well as Postgres when determining if the server is alive and ready to accept traffic (healthy).

Changes:

• new /liveness endpoint
• new /readiness endpoint
• new handler for determining if the server is healthy by querying both Postgres and Redis.
• provides happy path tests for the new endpoints
• updates all readiness & liveness checks in various deployment mechanisms (docker compose, digitalocean 1-click, kubernetes helm chart) to use the new endpoints.

To-do before merge:

Screenshots:

Validation of changes:

Checklist:

• My pull request follows the guidelines in the Contributing guide?
• My pull request does not duplicate any other open Pull Requests for the same update/change?
• My commits are related to the pull request and do not amend unrelated code or documentation.
• My code follows a similar style to existing code.
• I have added appropriate tests.
• I have updated or added relevant documentation.

References