Servicex

Following on from feedback from users, in this release the DatasetGroup accepts a list of datasets and forwards on _verbs_ like as_files, as_signed_urls, etc.

Better handling of the .servicex file and clean up messages

This release was developed in collaboration between BenGalewsky and gordonwatts - attempting to ready the library for broader use.

No longer restrict `pandas` to be version 1.X. Also, remove explicit support and CI testing for python 3.7, and add CI testing for 3.12.

Normally, due to the loss of functionality for 3.7, we'd call this `v3.0`, however that is reserved for the new version of the front end.

There should be no functional changes.

What's Changed
* Remove pandas restrictions by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/358


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/v2.7.2...v2.8.0

* ATLAS names some of its files `sample.root.1` - the `.11` confuses `uproot.dask` - added a more robust way of interacting

What's Changed
* Open with post-fix filename fails by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/338


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/v2.7.1...v2.7.2