Request to support multibranch-default plugin for DevOps

**What's it about?**

[pipeline-multibranch-defaults](https://github.com/jenkinsci/pipeline-multibranch-defaults-plugin) can allow users to set a default for many pipelines. So maintaining all pipeline scripts from one place could be possible.

This idea came from [Kubesphere Chinese forum](https://kubesphere.com.cn/forum/d/2889-jenkinsfile/3).

**What's the reason why we need it?**

I believe this is an important feature for Kubesphere. There're a few use cases:

* There're many pipelines that have very similar logic. It's hard to maintain all of them (for example 20+ pipelines).
* Sometimes the maintainers just don't have the permission to access the git server. For example, the tester team doesn't permission to access the business code base. It's very inconvenient in this case.
* ...

Please leave your comments below if there's anyone agrees with me. Or just give me a thumb up. Or you also can provide more use cases below.

Why do we need to support this via Kubesphere? Anyone can install this plugin into their Jenkins instead. But in our real world, it's not true. We don't really hope all team members can access Jenkins even have admin permission. So, providing some kind of way to maintain the default pipeline via Kubesphere is absolutely necessary.

But there's one more thing we need to consider. There're so many plugins that can be installed into Jenkins. Maybe we need to figure out a smart way to integrate some of them.

**Area Suggestion**

/area devops

/kind feature-request

Start by reviewing the pipeline-multibranch-defaults plugin and how KubeSphere currently exposes Jenkins pipeline configuration. Identify the integration boundary and the supported use cases, including centralized defaults and users without Jenkins or repository access. Done means a concrete integration design with agreed scope, installation assumptions, and validation criteria.

Written by the indexing model from the issue text.