Pytest-reana

- Changes CI to use the stable release of Python 3.12.

- Adds support for Python 3.12.
- Changes `apispec` dependency version in order to be compatible with `PyYAML` v6.
- Fixes container image fixtures to be Podman-compatible.
- Fixes Kombu documentation linking.

- Adds fixture providing example of user secrets needed for Kerberos tests.
- Adds support for Python 3.11.
- Fixes location of Celery docs for ReadTheDocs pages.
- Removes hard-dependency on `black` code formatter version.

- Adds support for Python 3.10.

- Adds nested Yadage workflow specification fixture.
- Adds empty workflow workspaces for sample workflows by default.
- Adds internal representation of a scatter-gather Snakemake workflow fixture.
- Changes `tmp_shared_volume_path` fixture to be configurable through environment variable.
- Changes fixtures to run with the full workspace path stored in the database.
- Removes support for Python 2.

- Changes internal dependencies to remove click.