Require confirmation before saving/setting room settings

### Description

Changing room settings can potentially have big effects. Encryption, room history, join rules, room aliases etc. Many users (such as myself) are not used to configuration GUIs which will enact big changes immediately on fiddling with settings. This may lead to Element users changing rooms settings "by accident", simply by playing around in the room settings.

In my opinion, being able to review changes and then consciously applying them is a "must" for big rooms, communities, spaces etc in general.

### Steps to reproduce

- Change any room settings, like just choosing another entry in the drop-down for room aliases.
- The main room alias is changed immediately

I would have expected each modified setting to be somehow marked to denote that it's been changed from the currently active config and then being able to press a save button to apply the changes.

### Version information

- **Platform**: desktop Element version: 1.7.28

The issue names no files, tests, or entry points; start by tracing the desktop room-settings flow, especially the room-alias dropdown and other settings that apply immediately. Done means users can review modified settings and explicitly confirm applying them, with the behavior covered by relevant tests.

Written by the indexing model from the issue text.