mugen test framework

**Please provide an in-depth description of the question you have**:

I found that there is a test framework called [mugen](https://github.com/kmesh-net/kmesh/tree/main/test#%E4%BB%80%E4%B9%88%E6%98%AFmugen) in Kmesh source code.

But it seems like it hasn't been updated for a long time.

**What do you think about this question?**:

It also looks like an integration test. How is it different from the e2e test we are about to merge?

If it can cover scenarios that e2e cannot cover, can it be added to CI?

If it is no longer used, can it be deleted from the source code?

**Environment**:
- Kmesh version: N/A
- Others: N/A

Start in the repository's test directory and read the Mugen documentation linked in the issue, then compare its integration-test scenarios with the e2e tests mentioned in the question. Done means documenting whether Mugen adds coverage, deciding whether to add it to CI or remove it, and carrying out the chosen repository change.

Written by the indexing model from the issue text.