Annoyingly, prometheus Registry collects metrics async, which is causing our test to be racy. They also don't export enough from the Metric interface for us to replicate a synchronous collect, so we have to use Eventually to test.
Adds prometheus metrics to PGPubsub for monitoring its health and performance in production.
Related to #11950 --- additional diagnostics to help figure out what's happening
* chore: add /v2 to import module path
go mod requires semantic versioning with versions greater than 1.x
This was a mechanical update by running:
```
go install github.com/marwan-at-work/mod/cmd/mod@latest
mod upgrade
```
Migrate generated files to import /v2
* Fix gen
* chore: rename store to dbmock for consistency
* chore: remove redundant dbtype package
This wasn't necessary and forked how we do DB types.
* chore: separate pubsub into a new package
This didn't need to be in database and was bloating it.
