[WIP] Python Middleware v2 Scaffolding

[lkingland]

This is a draft of the Python v2 middleware which supports the Scaffolding system.

/kind enhancement

[knative-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lkingland

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [lkingland]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[knative-prow-robot]

PR needs rebase.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[matzew]

how was that done before?

[lkingland]

These commands presume the binaries are available in PATH, and use the first match. This is common. However, a nice feature offered by some is to be able to override this on a case-by-case basis by setting environment variables such as MYAPP_PYTHON=/path/to/python. We also support this in some cases, but not consistently throughout. This might be a #good-first-issue

[matzew]

nice for getting this started