feat: retry initial MongoDB connections

[aldeed]

Resolves #5806
Impact: minor
Type: feature

Issue

When spinning up separate API and MongoDB containers, due to timing the API container may try to connect to MongoDB before it is fully ready. Now that API starts up faster in 3.0.0, this is more likely. The MongoDB driver library does not auto-retry connecting on the first connection.

Solution

Adds our own auto-retry logic for the first connection, as well as better logging about what is happening with db connections.

Breaking changes

None

Testing

1. Start api service but not mongo service. Verify that you see logging about retrying 10 times and it eventually gives up and exits the app with the error. (In a development environment, you'll see this whole series of connection logs twice because it first tries to auto-init the replica set.)
2. Start api service but not mongo service. While it's showing the retrying log messages in API logs, start the mongo service. You'll have about 30 seconds window to do so. Verify in the API logs that it eventually shows a successful db connection before it fully times out.
3. Start both api and mongo services normally. Verify that it shows a successful db connection in the logs on the first or second try.

[focusaurus]

🎉

[willopez]

LGTM, works as advertized