Instead of acquiring a connection per service per request, we
acquire connections more often but at a more granular level, meaning
they're also disposed of more quickly instead of staying for a long time
in case of long-running commands or leaks.
This also refactors a large portion of the DI toolchain, since
I discovered that you shouldn't be reusing IDbConnection objects.
Instead, most services and stores are now declared transient, and
the webhook cache has been moved to a database-independent storage
singleton by itself.
