Rename partition to session

[emmuhamm]

Description

Fixes #32

Needs to go in with the associated change in drunc#892

Maintains backwards compatibility with the old 'partition' in two ways:

• the retract-partition function still exists, redirects to retract-session, logs a warning just in case
• the payload first checks for session, and then partition, raises if nothing is found. Also raises an error if both session and partition are defined in the payload.

Pytest added to check for backwards compatibility

TODO

• Check on the full integ test
• Get pawel's review first
• Tell Kurt about this :)

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature or enhancement (non-breaking change which adds functionality)
• Optimization (non-breaking change that improves code/performance)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Testing checklist

• Unit tests pass (e.g. dbt-build --unittest)
• Minimal system quicktest passes (pytest -s minimal_system_quick_test.py)
• Full set of integration tests pass (dunedaq_integtest_bundle.sh)
• Python tests pass if applicable (e.g. python -m pytest)
• Pre-commit hooks run successfully if applicable (e.g. pre-commit run --all-files)

Nothing special, just clone this repo and the PR for drunc linked above and run a simple drunc session on yourself and see if the connsvc works just fine.

Further checks

• Code is commented where needed, particularly in hard-to-understand areas
• Code style is correct (dbt-build --lint, and/or see https://dune-daq-sw.readthedocs.io/en/latest/packages/styleguide/)
• If applicable, new tests have been added or an issue has been opened to tackle that in the future.
  (Indicate issue here: # (issue))

[emmuhamm]

Still waiting on the results of the integ test, but a preliminary look (not full review) would already be appreciated