Research: Get the JUnit test results from external storage instead of Jenkins

I didn't have enough information for this. But it looks like worth supporting it in KubeSphere DevOps.

## References

* [Introducing external storage for JUnit test results](https://github.com/jenkins-infra/jenkins.io/pull/4505)

Start with the linked Jenkins reference on external JUnit test-result storage and determine how that capability relates to KubeSphere DevOps. Identify the affected integration entry points and document the required scope, dependencies, and acceptance criteria before implementation.

Written by the indexing model from the issue text.