This change matches existing settings, and is thus a no-op.  Tested
against existing configuration.

`configure-projects` uses the python-gitlab project to loop over all
projects in the instance and disable issues and wikis.

This also adds a requirements.txt and some rudimentary instructions in the
README.

Moves user-facing commands and configuration to top of repo, moves a few
common functions into a util.py.

Make `apply-settings` send JSON in the request body, which enables us to
set values that take an array.

Use that to handle restricted_visibility_levels and import_sources.

This commit reflects the current state of production settings.

Bug: T284336

Remove reference to wmf-gitlab-tools.

This seems like a better user experience overall than getting sent with no
explanation to an IDP login form.