[Doc] There are two pip-307s

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### What issue do you find in Pulsar docs?

I found that there are two pip-307s in the pip directory, which confused me.
Ones is:
https://github.com/apache/pulsar/blob/master/pip/pip-307.md
Other one is:
https://github.com/apache/pulsar/blob/master/pip/pip_307.md

### What is your suggestion?

Maybe we should rename one of the PIPs? Otherwise when we talk about PIP-307, people might not understand which PIP we are talking about.

### Any reference?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Compare pip/pip-307.md and pip/pip_307.md, then search the documentation for references to each name before deciding which naming should remain. Update the affected references so PIP-307 is unambiguous; done means one canonical file/name remains and its links resolve.

Written by the indexing model from the issue text.