We need to pin Flask dependencies for the user venv or it's almost guaranteed to break in the future

[carlosperate]

As partially done in this PR, which we only noticed because we were building Mu after Flask/Werkzeug v3 were released:
#2465

Flask (and other Pallets projects) don't pin/lock up versions, which is arguably a commonly accepted approach, but that means that all Flask users will need to do this to ensure future pip installs don't fail:

• Flask setup.py should use "Werkzeug ~= 2.2.2" instead of "Werkzeug >= 2.2.2" pallets/flask#5285

More than that, Pallets often pushes breaking changes in "minor" releases, as they don't follow semver:
https://blog.miguelgrinberg.com/post/some-more-to-talk-about-flask

So, it looks like we might have to do the pinning ourselves.

Of course, that means having the risk of current packages not being compatible with future OS/Python releases (for example, with different manylinux versions, or any binary packages that might specify cp3x compatibility instead of the generic abi3).