Implement circuit breaker in Rails Gitaly client for ResourceExhausted errors

What does this MR do and why?

Implements a circuit breaker pattern in Gitlab::GitalyClient to handle ResourceExhausted errors from Gitaly. When Gitaly returns capacity limit errors, the circuit breaker opens to reduce load and returns errors early without making additional calls.

This helps protect GitLab from cascading failures when Gitaly is under heavy load.

Key features

• Circuit breaker per service/rpc endpoint - Isolates failures so one endpoint's issues don't affect others
• Bypasses circuit breaker for authenticated requests - Only unauthenticated requests are throttled to avoid blocking logged-in users
• Handles both direct and stream responses - Works correctly for all Gitaly RPC patterns
• Released behind gitaly_circuit_breaker feature flag - Safe rollout with ability to disable if issues arise

Implementation details

1. New Gitlab::GitalyClient::CircuitBreaker class - Wraps calls with circuit breaker logic
2. Integration into Gitlab::GitalyClient::Call - Applies circuit breaker to all Gitaly RPC calls
3. Updated Gitlab::CircuitBreaker utility - Added exception: parameter for exception-based error handling

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/582826

MR acceptance checklist

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Follow-up items

• Add Prometheus metrics (https://gitlab.com/gitlab-org/gitlab/-/work_items/587646+)
• Configure thresholds based on analysis from #582823 (separate MR)
• Create feature flag rollout issue