Allow CKB users to cross reference EB documents

[Windvis]

Builds on #575 and allows CKB users to cross reference documents submitted by EBs they govern.

A new field is displayed in the relevant forms that makes it possible to search for documents in a similar fashion as the other cross reference field.

Related tickets
DL-6202, DL-6203, DL-6206, DL-6207

Test instructions

Basic happy flow

1. log in as an EB user that has a CKB. (Grobbendonk has both a CKB and 2 EB that belong to it)
2. create a new submission in toezicht with one of the following types and submit it:

• Jaarrekeningen
• Budget(wijziging) - Indiening bij centraal bestuur of representatief orgaan
• Meerjarenplan(aanpassing)

3. log out and log back in as the corresponding CKB
4. create a new submission in toezicht with the type that corresponds to the submission you made before:

• Jaarrekeningen van besturen van de eredienst
• Budgetten(wijzigingen) - Indiening bij representatief orgaan
• Budgetten(wijzigingen) - Indiening bij toezichthoudende gemeente of provincie
• Meerjarenplannen(wijzigingen) van de besturen van de eredienst

5. You should see a "Gerelateerde documenten" field
6. click the "Voeg documenten toe" button
7. select the EB that you used to create the submissions
8. select the submission and add it to the list (you should only see documents with the correct type, not all documents submitted by the EB)
9. save and reload the form
10. the table should load as expected again

[Windvis]

This file doesn't include the changes from this PR, since it wasn't merged when I generated this form. Before we merge this we should regenerate the form and update tho form.ttl so that those changes aren't lost.