test(source/cloudgda): migrate integration tests to MCP endpoint - #4205

Description

Migrates the cloudgda integration tests from the legacy /api endpoint to the MCP endpoint (/mcp), following #2922. The legacy REST tests are kept, and both transports share setup and assertions.

• Adds cloud_gda_mcp_test.go: MCP tools/list + invocation for the mock-backed cloud-gda-query tool, a tools/list check for the 9 conversational analytics tools, and the list/get/ask data agent checks over MCP.
• Refactors the legacy file into shared setup (startCloudGdaMockServer, setupConversationalAnalyticsTest, getConversationalAnalyticsToolsConfig) and a small REST/MCP transport, so the list/get/ask checks run against both endpoints.
• Resource cleanup uses t.Cleanup with bounded context.WithoutCancel contexts; the ask-agent retry loop is context-aware.

Testing: TestCloudGdaToolEndpoints and TestCloudGdaMCPToolEndpoints (in-process mock gRPC server) pass locally. The conversational analytics tests need a GCP project and ID token and are verified by the CI cloudgda job.

PR Checklist

Thank you for opening a Pull Request! Before submitting your PR, there are a
few things you can do to make sure it goes smoothly:

• Make sure you reviewed
  CONTRIBUTING.md
• Make sure to open an issue as a
  bug/issue
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
• Ensure you have manually reviewed the entire diff before requesting a
  review
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Make sure to add ! if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>