Ruler: Make the sync queue polling intervals configurable.

[stevesg]

In some environments, it may be desirable to trade off increased resource usage for faster rule group updates.

• For the outbound queue - polling more often results in more gRPC calls to other rulers, but nothing else. I think reducing this below 10s could be valuable.
• For the inbound queue - polling more often results in more rule sync operations, which can be quite expensive for tenants with many rule groups. Reducing this is likely not a wise idea.

In a follow up PR, I want to experiment with making the sync operations more specific (e.g. include rule group), this would potentially allow more frequent inbound queue polling.

Part of #9329

[gotjosh]

LGTM

[gotjosh]

Remember to modify the about versioning documentation.

[tacole02]

😄