`ContentLibraryPermission` refers to `ContentLibrary` with a `related_name` of `permission_grants`, which should be used in ManyRelation instead of the lowercase model name (see [docs](https://bridgekeeper.readthedocs.io/en/latest/api/rules.html#bridgekeeper.rules.ManyRelation))
This PR changes a blockstore based API, which is not part of the devstack yet. To test this:
From the blockstore directory, run `make testserver` to start a test-specific instance.
From `make studio-shell` run: `EDXAPP_RUN_BLOCKSTORE_TESTS=1 python -Wd -m pytest --ds=cms.envs.test openedx/core/djangoapps/content_libraries/tests/`
[ ] @bradenmacdonald
[ ] edX reviewer[s] TBD