Define Python packaging policy and best practices

[ermo]

There are ongoing experiments related to packaging Python in the temporary snekpit/venom recipe repository.

These experiments have uncovered a number of issues that need to be addressed.

This issue is meant as a tracker issue for sub-tasks that need to be resolved before we're happy with our Python packaging policy and associated tooling requirements.

Existing tasks:

• Decide a consistent URL for Python sources snekpit/venom#5

PRs:

• macros/actions/python.yml: Use correct python deps #36

[ermo]

@sunnyflunk:

I'm tentatively assigning this to you. If you don't feel like now is the correct time to take a look at it for whatever reason, just unassign yourself and we can pick it up at a later point. =)

[sunnyflunk]

Essentially what needs to happen is to determine a bootstrap process that can apply to any bootstrap (say having $pkg/stone-stage1.yml as a 1st bootstrap build and then rebuild the stone.yml's once the -stage1's are all done). This will be essential for bringing up new architechtures and being consistent across all tooling and packages will make things a lot simpler.

The 2nd step is then to apply the bootstrap process to the python packages as it will need rebootstrapping with every version upgrade.