Servicex

- Allow for a "type" of backend when we create the `ServiceXDataset`
- Allow for multiple servicex backends to be specified in a .servicex file

This breaks the current user interface:

- You have to specify a `type` of backend when you create the `ServiceXDataset`
- If you use a `.servicex` file, you'll need to change the format so you can have multiple servicex endpoints in there.

While this release was built, and it does contain changes, we decided to back out the changes that broke the old UW - so we can go back to the 2.1 series.

What's Changed
* ci: Use trusted publishers for publishing to PyPI by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/353
* build: Remove nest-asyncio from core dependencies by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/356
* Multiple xrootdfiles by BenGalewsky in https://github.com/ssl-hep/ServiceX_frontend/pull/359


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/3.0.0-alpha.14...3.0.0-alpha.15

Try out trusted publisher

What's Changed
* fix: Add CLI entrypoint by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/350


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/3.0.0-alpha.11...3.0.0-alpha.13

What's Changed
* feat: Use hatchling as the build backend by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/349

What's Changed
* feat: Use hatchling as the build backend by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/349


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/3.0.0-alpha.9...3.0.0-alpha.11