Provide frozen requirements.txt files for images, and automation to update them

[consideRatio]

This PR makes our Dockerfiles build from frozen Dockerfile.requirements.txt files to provide a git history of what is installed in the images. It also adds a github workflow to automatically refreeze the requirements.txt file with the click of a button.

I'm not sure if adding this complexity is worth the benefits, but if it isn't the work I've invested in this PR is something I can benefit on in other projects where its more critical to have a version controlled history of whats part of images.

Pros

• Version controlled history of python packages installed in images.
• Closes Provide frozen requirements.txt based on requirements.in for Dockerfiles #574
• Closes Document the version of Dask associated with images for helm charts? #161

Cons

• Helm chart tests will be based on frozen dependencies
• Even with automation in place to refreeze, its still work added.
• The automation could need maintenance
• The entire setup adds complexity for people looking to understand how things work

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PR tested to work in a fork. Test failures are unrelated and fixed by #573.