Have a separate category `collectives` for our setup checks

[max-nextcloud]

Is your feature request related to a problem? Please describe. Admin was confused by these setup checks:

occ setupchecks
	database:
		✓ PDO SQLite driver: PDO SQLite driver is enabled, full text search of page content is available.
		✓ Database missing columns: None
		✓ Database missing indices: None
		✓ Database missing primary keys: None
		✓ Database pending bigint migrations: None
		✓ MySQL Unicode support: MySQL is used as database and does support 4-byte characters
		✓ Scheduling objects table size: Scheduling objects table size is within acceptable range.
		✓ Database version: 10.6.18-MariaDB-0ubuntu0.22.04.1
		✓ Database transaction isolation level: Read committed
	app:
		✓ Teams App Enabled: Teams app is enabled

Did not know where they came from. Having a collectives category would make that clear right away. Other apps do so too:

	talk:
		✓ Talk configuration values
		✓ High-performance backend
		✓ Federation
		✓ Recording backend
		✓ SIP configuration
		✓ Background blur
	ldap:
		✓ Invalid LDAP UUIDs: None found
		✓ LDAP Connection: Binding and searching works on the configured LDAP connection ()
...

Describe the solution you'd like Add our setup checks under the collectives category.