[Controller] Add gRPC support for isStoreMigrationAllowed API

[pthirun]

Problem Statement

As part of the controller gRPC migration, the isStoreMigrationAllowed API needs to be available via gRPC while maintaining the existing HTTP endpoint during the migration period. This follows the same pattern established by other controller API migrations, where business logic is abstracted so both HTTP and gRPC can share the same implementation.

Solution

Added gRPC support for the isStoreMigrationAllowed API following the established migration pattern:

1. Proto definitions (ClusterAdminOpsGrpcService.proto): Added isStoreMigrationAllowed RPC method with IsStoreMigrationAllowedGrpcRequest and IsStoreMigrationAllowedGrpcResponse messages
2. Request handler (ClusterAdminOpsRequestHandler.java): Added isStoreMigrationAllowed() method that validates parameters and calls admin.isStoreMigrationAllowed(), returning a gRPC response
3. gRPC service implementation (ClusterAdminOpsGrpcServiceImpl.java): Added isStoreMigrationAllowed() override (no ACL check needed - any user is allowed to check migration status, matching HTTP endpoint behavior)
4. HTTP route update (ClusterRoutes.java): Updated to convert HTTP requests to gRPC format and delegate to the shared handler
5. Route registration (AdminSparkServer.java): Updated to pass the request handler to the route

The implementation reuses the existing business logic in Admin.isStoreMigrationAllowed(), ensuring consistency between HTTP and gRPC endpoints.

Code changes

• Added new code behind a config. If so list the config names and their default values in the PR description.
• Introduced new log lines.
  • Confirmed if logs need to be rate limited to avoid excessive logging. (Info level logging only, consistent with other gRPC endpoints)

Concurrency-Specific Checks

Both reviewer and PR author to verify

• Code has no race conditions or thread safety issues. (Stateless request handling, delegates to existing thread-safe Admin methods)
• Proper synchronization mechanisms (e.g., synchronized, RWLock) are used where needed. (N/A - no shared mutable state)
• No blocking calls inside critical sections that could lead to deadlocks or performance degradation. (N/A - no critical sections)
• Verified thread-safe collections are used (e.g., ConcurrentHashMap, CopyOnWriteArrayList). (N/A - no collections introduced)
• Validated proper exception handling in multi-threaded code to avoid silent thread termination. (Uses handleRequest() utility for consistent error handling)

How was this PR tested?

• New unit tests added.
  • Request Handler Tests (ClusterAdminOpsRequestHandlerTest.java):
    • testIsStoreMigrationAllowedReturnsTrue - Verifies handler returns true when migration is allowed
    • testIsStoreMigrationAllowedReturnsFalse - Verifies handler returns false when migration is not allowed
    • testIsStoreMigrationAllowedInvalidCluster - Verifies handler throws exception for invalid input
  • gRPC Service Tests (ClusterAdminOpsGrpcServiceImplTest.java):
    • testIsStoreMigrationAllowedSuccess - Verifies gRPC layer returns correct protobuf response
    • testIsStoreMigrationAllowedReturnsFalse - Verifies gRPC layer handles false value correctly
    • testIsStoreMigrationAllowedError - Verifies gRPC layer maps exceptions to INTERNAL status
  • HTTP Route Tests (ClusterRoutesTest.java):
    • testIsStoreMigrationAllowedReturnsTrue - Verifies HTTP layer converts to/from gRPC correctly
    • testIsStoreMigrationAllowedReturnsFalse - Verifies HTTP layer handles false value correctly
    • testIsStoreMigrationAllowedError - Verifies HTTP layer sets error flag on exception
• New integration tests added.
  • Integration Test (TestControllerGrpcEndpoints.java):
    • testIsStoreMigrationAllowedGrpcEndpoint - End-to-end test with real Venice cluster
• Modified or extended existing tests.
• Verified backward compatibility (if applicable). (HTTP endpoint unchanged, gRPC is additive)
• Unit test coverage verified: 100% instruction coverage for all new methods

Does this PR introduce any user-facing or breaking changes?

• No. You can skip the rest of this section.
• Yes. Clearly explain the behavior change and its impact.

[sushantmane]

Overall LGTM few minor comments

[sushantmane]

LGTM