build: pin pip version to resolve pip-tools conflict

[marlonkeating]

This pull request addresses compatibility issues with pip and pip-tools by pinning the pip version and updating related tooling and dependencies. It also upgrades several Python package versions across multiple requirements files to ensure the project stays current and secure.

Dependency and Tooling Updates

• Pinned pip to <25.3 in requirements/constraints.txt to resolve incompatibility with pip-tools and prevent build failures. Explanatory comments and tracking issue references were added.
• Upgraded pip-tools to 7.5.2 in requirements/dev.txt for improved compatibility.
• Added logic in Makefile to download common_constraints.txt and clean up constraint conflicts with Django and django-simple-history during upgrades. [1] [2]
• Updated the upgrade and requirements installation workflows in Makefile to ensure proper constraints and package installation order.
• Documented the pip pinning and build fix in the changelog (CHANGELOG.rst).

Python Package Upgrades

• Upgraded major packages such as Django (4.2.25 → 5.2.8), pytest (8.4.2 → 9.0.1), redis (6.4.0 → 7.1.0), and many others across requirements/base.txt, requirements/dev.txt, requirements/doc.txt, and requirements/ci.txt to their latest compatible versions. [1] [2] [3] [4] etc.)

Miscellaneous Dependency Updates

• Updated various other dependencies for bug fixes and security, including certifi, click, faker, psutil, pymongo, pynacl, stevedore, tox, and virtualenv in all relevant requirements files. [1] [2] [3] [4] [5] etc.)Description:
  Describe in a couple of sentences what this PR adds
  Link to the Jira ticket, if applicable.

Testing instructions:
Add some.

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

Post merge:

• Create a tag
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)