[Usabillity] In progress permissions are not saved

_Opening this issue after discussing and as suggested by @bosschaert_

### Problem
In progress permissions are not saved. Any permissions configuration which is not "Save"d is lost if navigating away from the permissions sheet.

### Steps to reproduce
1. Open the permissions sheet
2. Add some permissions
3. Leave without saving
4. Open the permissions sheet again

All unsaved work is lost.

### Expected outcome
Not fully clear...

On one side, it may be a non problem and a doc warning is sufficient (maybe combined with a rename of `Save` -> `Activate`).

Another approach could be to use a 2 step activation process, inline with the Helix Config, where any change you write in the sheet is automatically saved so nothing gets lost, but they only take affect when you `Activate`.

Of course this can create the question of: "what changed?" between what's in the sheet and what's activated.
Which could be solved with a read-only `active-permissions`, as a separate iteration if customers ask.

No files, tests, or entry points are named. Reproduce the loss through the listed permissions-sheet steps, then clarify whether the outcome should be a warning, a Save-to-Activate rename, or automatic saving with separate activation. Done requires an agreed behavior and verification that leaving and reopening the sheet preserves or intentionally discards changes.

Written by the indexing model from the issue text.