Add readiness and liveness probes

[garryod]

Adds readiness and liveness probes to the backend and frontend Deployments

[GDYendell]

This should help with failed upgrades, but does this determine readiness based on the catalog being fully populated? If not it will still result in downtime because although the readiness check will pass the dev guide won't be available. Maybe this can be improved in a future change.

[garryod]

This should help with failed upgrades, but does this determine readiness based on the catalog being fully populated? If not it will still result in downtime because although the readiness check will pass the dev guide won't be available. Maybe this can be improved in a future change.

The readiness of the backend is based on the healthcheck endpoint being available, which it won't be if it can't establish a connection to the DB