Edx-organizations

api.bulk_add_organizations` and `api.bulk_add_organization_courses` previously logged the organizations and organization-course linkages they were about to create/reactivate.

This was somewhat helpful, but parsing the log output by hand is more time-consuming and error prone than simply returning the data and allowing the caller decide how to process it

Part of [TNL-7774](https://openedx.atlassian.net/browse/TNL-7774).

We originally checked the deprecated `FEATURES['ORGANIZATIONS_APP']` setting as an alternative to the new `ORGANIZATIONS_AUTOCREATE` settting, but since we're going to give `ORGANIZATIONS_AUTOCREATE` a default value in edx-platform anyway, the fallback check will never even be reached. Having the fallback check in the edx-organizations codebase is more misleading than anything else.

This is effectively a no-op change.

Related to [TNL-7646](https://openedx.atlassian.net/browse/TNL-7646).

Fixes database queries in `api.bulk_add_organizations` and `api.bulk_add_organization_courses`.

Part of [TNL-7646](https://openedx.atlassian.net/browse/TNL-7646).

api.bulk_add_organizations` and `api.bulk_add_organization_courses` each take an new optional boolean argument: `dry_run`.

When `dry_run==True`, the bulk-add functions will log what organizations and organization-course linkages *would* be created or reactivated,
but they will not apply the changes to the database.

Part of [TNL-7646](https://openedx.atlassian.net/browse/TNL-7646).

Two new functions were added to `organizations.api`:
* `bulk_add_organizations(organization_data_items)`
* `bulk_add_organization_courses(organization_course_pairs)`

Both use Django's `bulk_create` and `bulk_update` functions to allow insertion of many rows in a constant number of queries. They will aid in the creation of the upcoming edx-platform `backfill_orgs_and_org_courses` management command.

The release also resolves some trivial `RemovedInDjango40Warning`s.

No breaking changes since 6.0.0.

Part of [TNL-7645](https://openedx.atlassian.net/browse/TNL-7645).

The `short_name` field on the `Organization` model has been made unique.

This makes the model reflective of a reality that already exists on edX.org, and realizes an informal assumption that we make throughout edx-platform code.

For Open edX instances that enable `FEATURES['ORGANIZATIONS_APP']`, running this migration will fail if you have rows in the LMS/Studio `organizations_organization`table with identical values of `short_name` (noting that "identical" is case-insensitive for MySQL). If your instance has organizations with identical `short_names`, the easiest fix is to delete conflicting rows via Django admin (making sure that they have no inbound references from other model instances), and the re-attempting to run the migration. You probably would have wanted to do this anyway.