This adds two new config options for the `database` stanza:
- `max_idle_connections`
- `max_idle_time`
These correspond to settings for the underlying `sql.DB` instance. They
can be used to have finer control over the controller's database
connection pool. For example this can be used to mitigate the high
connection overhead when connecting to postgres by setting a high
`max_idle_connections` and either setting `max_idle_time` to zero or to
a high duration.
Alternatively, if using a connection pool like pgpool-II or pgbouncer,
`max_idle_connections` can be set to 0.
See:
https://pkg.go.dev/database/sql#DB.SetMaxIdleConns
https://pkg.go.dev/database/sql#DB.SetConnMaxIdleTime
https://www.pgpool.net/mediawiki/index.php/Main_Page
https://www.pgbouncer.org/