12/misc/initial release/2.0.0-pre1 (#13)

* LICENSE.md: Add linebreak

* Fix circular import when using FlexFieldsFilterBackend in Django settings

* Rename settings variable REST_FLEX_FIELDS to REST_FLEX_FIELDS2

* Fix potential endless recursion in OpenAPI generation

* Unit tests for recursive expandable fields

* Finish removal of package-level imports

* Reflect API changes in the unit tests

* Rename maintainer docs files

* Unify docstrings

* Fix warnings by CodeQL scan

* Finish manual code review

* Refine dependency policy (more suitable for reusable lib)

* Document and refine dependency policy

* Upgrade poetry.lock

* Fix warning in docs/guide/advanced.rst

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fix typo in README.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fix package-level imports in docs

* CoPilot warning: Use tuple for _get_expandable_fields

* Clarify PR/branches in the release checklist

* Update src/rest_flex_fields2/filter_backends.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update docs/maintainers/versioning-and-releases.rst

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* README.md: Better migration steps

* Copilot flagged doc warnings

* Copilot flags space after tripple quotes

* Handle __all__ in schema example generation

* Update .github/workflows/run-tests-full.yml

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Docs: Fix markup

* Some more Copilot warnings

* Update .vscode/settings.json

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Even more pendantic doc warnings

* Remove Django version classifier in pyproject.toml

* Copilot getting on my nerves

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>