The OpenAPI docs (at /api-docs) for the modulestore_migrator app were missing
some info, had duplicated info, and had some incorrect info. This brings them
up to a state where they're accurate and should have all the info needed for
someone to integrate with the API. For example:
* We move the viewset class docstrings, which have the info needed for someone
to POST correctly, into the actual POST handler method docstring. That way,
they show up under that POST API endpoint rather than the GET API endpoint.
* We fix the target keys to be v2 keys instead of v1 keys. We add detail on
all the different migration options and why a user would want to specify
them.
* We fix the docs for `parameters` field to explain that they are always
a _list_ of parameter objects, even for non-bulk migration tasks.
This also removes confusing & unnecessary endpoints:
* POST /api/modulestore_migrator/v1/bulk_migration/cancel
* DELETE /api/modulestore_migrator/v1/migrations/<uuid>
Finally, it sorts this endpoint to be newest-first:
* POST /api/modulestore_migrator/v1/migrations
Fixes: https://github.com/openedx/edx-platform/issues/37566
ec1d9593d9