Instrument database calls made by CTMS

[jwhitlock]

From #124 (comment):

What would be great to see in the next phase is instrumentation around any outgoing requests you have. I know the webapp talks to postgres, I'm less sure if it talks to other systems like Acoustic directly. For anything it does talk to, having a counter for the total requests and a histogram of response time, both broken down by success vs error, would be helpful for debugging.

A quick search finds https://pypi.org/project/query-exporter/, which seems to be designed for comparison of databases rather than monitoring database traffic. I think we'd need to write our own code, and use SQLAlchemy's hooks, similar to StatementWatcher in the CRUD tests.

My assumption is that the database is responsible for the bulk of the API request time, and the API errors, so API request timing is a first approximation of SQL query time.

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