fix: path validation in `microfrontends.json` (#11006)
### Description
Ensuring our path validation aligns to
https://github.com/pillarjs/path-to-regexp.
I'm also updating docs and the `with-microfrontends` example here.
### Testing Instructions
- Added tests that match path-to-regexp behavior.
- You can also test the changes against a sample repo.
<sub>CLOSES TURBO-4931</sub>