* Connection Diagnostics: Postgres Database tester
When adding a new resource using the Web UI we want to allow users to
test connecting to it.
We have two connection testers already:
- for SSH Nodes
- for Kube clusters
This PR adds a third tester: Postgres Database.
Most of the required changes for any Database are already present but
we're focusing on Postgres for now. Other databases will be added as
future PRs.
Testing a Database is similar to the other tests:
- generate certs for the logged in user
- connect to the resource using those certs
When generating the certificate, we inject an ID so that the Database
Service can add Connection Diagnostic traces.
