[meta] private-etc rework

[kmk3]

Currently #5610 is used for the discussion of the new private-etc groups and associated refactoring.

Though unlike issues, when referencing a discussion a timeline event for the reference is not created, so links between discussions and issues/PRs/commits have to be created manually in comments (see https://github.com/orgs/community/discussions/2971).

So create this new issue to use as the main issue to be referenced in this case for the sake of automatic links.

Main discussion:

• 5610

Part of the rework:

• 6400

• 5518

• 5608

• 5609

• 5629

• 5638

• 5641

• 5642

• 5643

• 5650

• 5681

• 5737

• 5844

• 5989

• 6016

• 6104

• 5655

• 6435

• 6514

• 6515

Bugs:

• 5929

• 6094

Related:

• 2093

• 5591

• https://github.com/netblue30/firejail/discussions/5597#discussioncomment-4739664

• 5607

• 5645

• 5651

• 5996

• 6070

Kind of related:

• 5777

• 5884

• 5656