Jaeger v2.21.0 introduces breaking changes to query and configuration defaults

The release of Jaeger v2.21.0, as detailed in the project's GitHub release notes, includes several breaking changes that may affect existing deployments. Notably, the v1 HTTP endpoints in the query service have been removed, as they are no longer used by the UI. Additionally, the `ai.enable_mcp` configuration has been replaced with an optional `ai.mcp` config block. The release also introduces stricter validation by rejecting five unsupported Elasticsearch configuration keys at startup. Furthermore, the ClickHouse storage feature gate has been promoted to stable, signaling its readiness for broader adoption.

Operators planning to upgrade should carefully review their configurations and dependencies. Systems relying on the removed v1 HTTP endpoints will need to adapt to the newer API structure, which may require changes in custom integrations or third-party tools. Similarly, any configurations using the deprecated `ai.enable_mcp` setting must be updated to the new `ai.mcp` block format to avoid startup failures. Elasticsearch users should verify their configuration files to ensure none of the rejected keys are present, as this could prevent the backend from initializing. These changes reflect a broader trend in projects to streamline APIs and enforce stricter validation, often improving long-term maintainability at the cost of backward compatibility.