feat: implement automatic region failure detector registrations

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA.

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What's changed and what's your intention?

This PR adds automatic region failure detector registrations. The metasrv now automatically discovers and registers failure detectors for all regions found in table routes, and ensures that metasrv leader will only register once throughout its lifecycle.

Configuration changes:

• Add region_failure_detector_initialization_delay option.
  This delay helps prevent premature initialization of region failure detectors in cases where cluster maintenance mode is enabled right after metasrv starts, especially when the cluster is not deployed via the recommended GreptimeDB Operator. Without this delay, early detector registration may trigger unnecessary region failovers during datanode startup.

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[fengjiachun]

LGTM