build: Creating a missing workflow file `add-remove-label-on-comment.yml`.

The .github/workflows/add-remove-label-on-comment.yml workflow is missing or needs an update to stay in
sync with the current standard for this workflow as defined in the
`.github` repo of the `openedx` GitHub org.

build: Creating a missing workflow file `self-assign-issue.yml`.

The .github/workflows/self-assign-issue.yml workflow is missing or needs an update to stay in
sync with the current standard for this workflow as defined in the
`.github` repo of the `openedx` GitHub org.

Team no longer exists. See <https://github.com/edx/edx-arch-experiments/issues/132>.

The Community Engineering team has agreed that we would only like to get tagged on Python upgrade notifications, not paged in Ops Genie. This PR removes OG notification and also removes the team-reviewers as that was not working; we are moving to being tagged in the CODEOWNERS file.

Background
==========
As part of our Squad-based ownership, we should stay on top of what
happens in these repositories. However, due to the number of
repositories (and subsequently pull requests) across the edX ecosystem,
it is challenging to stay on top of notifications, separating the
'signal' from the 'noise'. Email filters can go a long way to taming
Inbox notifications, but this is manual and requires maintenance as
Squad ownership changes. It also fails to account for Github-specific behavior.

Proposal
========
By leveraging Github support for `CODEOWNERS` files [1],
we can ensure that our team is at least CCed explicitly, here,
in the form a requested review. This request is just that, a request,
not a requirement; we are not enacting any new merge requirements
at this time.

- [1] https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners

s/teaching-and-learning@edx.opsgenie.net/community-engineering@edx.opsgenie.net/