Request: Make it possible to disable schema check when connecting to a tenant

[senny]

The current PostgreSQL adapter checks if the schema exists whenever the tenant is changed. Our application connects to a new tenant on every request. While the schema check is usually fast, with a high request throughput it starts to add up. Summed up per day, our database spends a lot of time verifying the same thing over and over again.

We have a fixed list of available tenants. We need to restart anyway when we add a new tenant. At the point where Apartment.tenant_names includes a tenant, we are certain that the schema exists. And if not, it's fine to blow up.

It would be great if there was a possibility to disable this check with a configuration of sorts.

[mikecmpbll]

i'm in favour of this. there's been a PR for this already (#411) but the implications weren't sufficiently explored imo and not being a pg user myself, i wasn't confident that it wouldn't cause problems.

if you can add to this work to make it configurable, i would be more than happy to merge that.