GN-5323: include 'toegevoegde schepen' in IVGR8 mandatee table

[elpoelma]

Overview

This PR ensures that we include people with the 'Toegevoegde schepen' mandate in the 'Verkozen schepenen' table of IVGR8 (IVGR8-LMB-1-verkozen-schepenen)

connected issues and PRs:

GN-5323

How to test/reproduce

• Start the frontend
• Login as a municipality which contains a 'Toegevoegde schepen' in LMB
• Create/open an IV
• Sync the meeting
• In AP7: the 'toegevoegde schepen' should not be included in the tables (they are not known yet by that time)
• In AP8: the 'toegevoegde schepen' should be included in the table

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations