Restore floating Flask / Werkzeug dependency

[dbutenhof]

Werkzeug 2.3.1 appears to have resolved our problems using Flask 2.3.x, so restore the original floating dependency on flask.

This doesn't address the issue of whether we want to evaluate setting explicit dependencies across the board; the risk is that this forces us to periodically re-evaluate and update to avoid obsolescence and CVE problems, while the benefit is we don't have the sort of fun surprises recently delivered to us by flask and keycloak-js...

[webbnh]

This looks fine to me; however, given our recent experience, should we be placing a minimum on Flask and/or Werkzeug? (We really don't want Werkzeug 2.3.0....)

[dbutenhof]

This looks fine to me; however, given our recent experience, should we be placing a minimum on Flask and/or Werkzeug? (We really don't want Werkzeug 2.3.0....)

That's a conversation worth having another day, and in a more general context across our requirements.txt and package.json dependencies. This just restores what we had before, which will now give us Flask 2.3.1 and Werkzeug 2.3.1. We're more likely to run afoul of another incompatible upgrade than in a sudden downgrade.