privilege: allow batch builder to be assigned

[jechols]

Fixes v5.0.0 bug where nobody could get the new Batch Builder role. (Administrators have all privileges, so this didn't seem like a problem in our case, as admins are the ones who would build batches)

Normal contributors

I have done all of the following:

• [x] Fixes and new features have unit tests where applicable
• [x] A new changelog has been created in changelogs/ (based on changelogs/template.md)
• [x] Documentation has been updated as necessary (hugo/content/)