Add support to `--build-constraint(s)` flag for our constraint preparation

[potiuk]

Currently in airflow CI process we prepare constraints automatically and both our CI process and user installation are designed around using it to "stabilize" both CI (PR stability) and Reproducible installation of airflow.

This prevents Airflow from being susceptible to breaking installation and tests when new version of a dependency (including transitive dependencies) is released. We can detect such breakages and remedy and report them thanks to our canary builds, without impacting stability of regular PRs. Also our users can (almost - see below) reliably install airflow reproducibly.

However (as evidenced by pypa/setuptools-scm#1194 and pypa/setuptools-scm#1191 - when installing packages, the build isolation feature causes that installing 3rd-party packages from sources might be broken simply by a fact of releasing their build dependencies.

Uv already has --build-constraint flag and there is work on-going on adding similar flag to pip - pypa/pip#13534, and we should be able to come out with automation that gathers information about current version of build tools used for all our ".sdist" dependencies and freezes it to a separate "build-constraints" files alongside regular constraints.

That should make us resilient to future cases like that (while still allowing us to quickly detect and report such cases with our canary builds.

[notatallshaw]

FYI, it's not clear what is best practices for build constraints, it might be the case you can pin them all, alternatively you might just be able to put upper bounds or ranges on them.

And there is likely a difference between dev workflows (which can be somewhat scripted) and user workflows which need to "just work".

As this is an area not well historically served by Python package installer tools there is a lot less experience out there.

[potiuk]

FYI, it's not clear what is best practices for build constraints, it might be the case you can pin them all, alternatively you might just be able to put upper bounds or ranges on them.

Yep I know. It's just our choice and we have good reasons for Airlfow to do so.