Post-MVP department permissions

### As a Joplin user, I want permissions to be tied to my department, so I have access to content that is relevant to me.

- Future state, we’re thinking only moderators and admins will be assigning pages to the IA.

### As an author, I only want to see topic and topic collections within my department so I don't have to view topics that aren't relevant to my content.
- [ ] When authors go to select a topic for new pages they should only see topics from their department.

Notes (not synthesized) https://docs.google.com/document/d/154RQ3aIliIjcyk_Wd2MD74wo4OAHq1Xt9GjL8ik4o2Y/edit#
- Re: Topic control from Mass.gov https://massgovdigital.gitbook.io/knowledge-base/content-types-1/topic-pages/about-topic-pages

Currently topics aren't associated with departments. However, in order to prevent the average user from viewing topics that aren't relevant, we should constrain the view of topics to those that are currently associated with pages created by that department.

- [ ] Similar to #3085, this checkbox allows viewing of all topics across Alpha.


### even more notes
- [ ] When using a guide or internal link page picker, editors and moderators can filter out pages that belong/don't belong to their assigned department
- [ ] When an editor or a moderator creates a new page, the department(s) they are assigned to are automatically selected on the content page's department picker
- Question for **design and content**: I wonder if we should wait on this until we do more research about the editorial flow (and maybe understand how Drupal currently has departments implemented). Will there be instances in which moderators might have access to multiple departments' content? How would a department auto-appear on a content page in that instance?
- [ ] Ability to be editor from one department and a moderator in another department

**Other/future**
- Let's understand how these permissions are currently implemented in Drupal 8 and how our proposed implementation stacks up.
- Expiration date on permissions?
- Ability to view (but not edit) pages outside of your department)??? Need to do more research before we can try to solve for this.

Start by reviewing the linked notes and the existing Drupal 8 department-permission implementation mentioned in the issue. Clarify which permission and content-selection behavior is in scope, including department assignment and topic visibility, before identifying the relevant entry points. The issue does not define a completed implementation or tests.

Written by the indexing model from the issue text.