Add configuration to limit teams and rooms counts

[Half-Shot]

This is still missing functionality to handle the removal of team clients Punting to #399

This PR does 4 things:

• It limits the number of bridged rooms that can be created by config.
• It limits the number of teams that can be connected.
• It exposes a flag for whether the configured instance allows private rooms to be bridged to channels.
• It exposes these limits in a config endpoint.

[jaller94]

Further worries, that I didn't to check:

• Admin rooms are not in the rooms table, right?
• We do remove rooms from the rooms table when they get unlinked, right?

[Half-Shot]

Admin rooms are not in the rooms table, right?

Correct.

We do remove rooms from the rooms table when they get unlinked, right?

Correct

[jaller94]

LGTM