Add upgrade-package Makefile target and GitHub workflow

[timmc-edx]

edx-platform has a Make target upgrade-package that upgrades a single Python dependency while keeping everything else as constant as possible. It also includes a GitHub workflow that calls upgrade-package, which makes a PR against a specified branch with the results of the upgrade.

We might like to include this functionality in all new repos.

Acceptance criteria:

• upgrade-package target added to Makefile of cookiecutter templates
• upgrade-one-python-dependency.yml workflow extracted to openedx/.github repo as a reusable workflow
• edx-platform updated to use the new workflow
• all existing repos that use the workflow updated to use the new workflow
  • useful search query if using new search: https://github.com/search?q=(org%3Aopenedx%20OR%20org%3Aedx)%20upgrade-one-python-dependency-workflow&type=code
• New workflow reference added to templates