What's changed?

Fixes #4447.

Problem

In HertzBeat v1.9.0, bulk pause requests send monitor IDs as URL query parameters. Large selections can exceed Tomcat's request-size limit, causing requests to fail before reaching the controller.

Changes

• Updated the Angular frontend to send monitor IDs in the JSON request body.
• Updated the backend controller to accept JSON-body IDs while preserving compatibility with existing query-parameter requests.
• Updated OpenAPI documentation to clarify the request format and backward compatibility.
• Added E2E regression tests covering large selections, invalid input, legacy requests, and cleanup.
• Adjusted the E2E request timeout to accommodate bulk monitor creation.

Verification

• Backend: 133 tests passed.
• Frontend: 3 tests passed.
• E2E: 74 tests passed, including 15 new cases.
• Successfully paused 300 monitors in a single JSON-body request and verified their states.
• Verified backward compatibility with existing query-parameter requests.
• Confirmed the regression tests detect failures against the original v1.9.0 controller.
• Checkstyle and git diff --check passed.

The E2E suite was executed locally against a running HertzBeat release build using the project's API-testing runner. Docker Compose execution was not performed.

Compatibility and risk

Existing query-parameter requests remain supported. The changes are limited to bulk pause functionality and do not affect other bulk operations.

The E2E suite takes approximately 5 minutes due to synchronous monitor initialization in v1.9.x.

AI assistance

None.

Checklist

• I have read the [Contributing Guide](https://hertzbeat.apache.org/docs/community/code_style_and_quality_guide).
• I have written the necessary doc or comment.
• I have added the necessary unit tests and all cases have passed.

Add or update API

• I have added the necessary [e2e tests](https://github.com/apache/hertzbeat/tree/master/e2e) and all cases have passed.