Optimize DB performance at the connection pool level

[i-norden]

Test the following, incorporate improvements:

• Increase MaxIdleConns

• Separate connection pools for backfill, sync, and serve processes

• Increase max_connections in postgresql.conf

• Prioritize sync db connections over backfill connections (sql/sqlx.DB does not provide this level of control natively, this is much more involved than any of the above)