API docs OOB migration can cause high CPU usage on codeintel-db

Created by: slimsag

From Erik:

The code intel DB used to be super calm but now is at really high load.

https://sourcegraph.slack.com/archives/CHXHX7XAS/p1633691411261600

This is due to two things:

1. Running the migration too frequently
2. The COUNT operation being expensive / not a materialized view