Make sure adhoc groups have a name.

[rtibbles]

Summary

• Ensure all adhoc groups are created with a name
• Adds an upgrade task to add a name to all existing unnamed adhoc groups

References

Fixes issue with adhoc groups not getting deserialized during syncs

Reviewer guidance

I couldn't do a simple change to the default behaviour for adhocgroups to allow deserialization of empty names.

I think it might be possible by overriding the full clean method of the AdHocGroup model, but it seemed good to get this in for now, and assess if follow up was needed.

---

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[bjester]

Looks good