Disallow any database calls, or connections in routes

This helps prevents database connections not dropped because connections
are held open. See also https://github.com/rails/rails/issues/44875

We achieve this by swapping out with an empty ConnectionHandler within
the block.

We also have add a SKIP_RAISE_ON_INTIALIZE_CONNECTIONS in case there is
any unforeseen issues. User can use this to skip this if we encounter
any bugs.

Also, raise if new connection pools established within block

Changelog: other