Initial n+1 query insight

- [x] Simple identifier

Presently, if there are 5 or more queries in a given list of the form `SELECT 'foos'.* FROM 'foos' WHERE 'foos'.'id' = 13 LIMIT 1`, that table is considered to be doing an n+1 query with those queries as the n. The bullet gem monkey patches AR for detection which is pretty messy and including it in shinji would be overhead. We'll try after the query detection.

- [x] model for tracking transactions with n+1s

- [x] Worker performs analysis on transactions, storing in DB

- [x] Setup insight; should link to eager loading docs / short tutorial