Servicex

Alpha release including
- `codegen` argument for multiple code generator support on the backend
- `backend_type` argument to have the `codegen` argument default to the correct value if not specified
- correct `codegen` naming conventions propagated from the config file
- changes fixing root-file/parquet handling

Alpha release including the `codegen` argument for multiple code generator support on the backend, and the changes now included in the master fixing root-file/parquet handling.

First (quick and dirty) implementation of an optional `"codegen"` argument to the ServiceXDataset constructor, to test the mutliple code generator functionality in the backend.
This is only a first implementation, next steps will include propagating a default codegen argument from the default config, overwritable by the user's `servicex.yaml` config file, and possibly more elegant modular propagation of different code generators based on the requested dataset type by the user.

Highlights

* New functions to access lists of files synchronously (or async)
* Bug fix to work with latest versions of `ServiceX` release - correctly deal with `parquet` and `root-file` format types
* Lots of minor technical fixes (see below).

Thanks to everyone that contributed!!

What's Changed
* Added functions to get URLs sync from request + corresponding tests by talvandaalen in https://github.com/ssl-hep/ServiceX_frontend/pull/245
* build: Support Python 3.7+ by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/246
* ci: Update to stable GHA versions by matthewfeickert in https://github.com/ssl-hep/ServiceX_frontend/pull/247
* Enable python 3.11 support, and remove 3.6 support. by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/256
* Do not request `parquet` when we want `root-file` by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/257
* Fix up to use proper name of the token by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/258
* Obey default data return formats by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/260
* Use root-file, not root as a filetype by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/261
* Update changes for release by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/262

New Contributors
* matthewfeickert made their first contribution in https://github.com/ssl-hep/ServiceX_frontend/pull/246

**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/2.5.4...2.6.1

Fixing up dualing file-types used internally for root (`root` and `root-file`). Now only `root-file` is used.

What's Changed
* Use root-file, not root as a filetype by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/261


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/2.6.1b3...2.6.1b4

servicex` will now correctly obey the default file formats when making pandas and awkward array requests.

What's Changed
* Obey default data return formats by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/260


**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/2.6.1b2...2.6.1b3