### Description
Per Slack thread: https://wikimedia.slack.com/archives/G8QAPHCTT/p1712787742192229
The name is confusing when client prefs is the way we are saving preferences (similar to user preferences), and it is something that will be used for many things other than the "appearance" menu that contains theme, width, font size, etc. One example of this confusion is the `vector-feature-client-prefs-pinned-clientpref-1` class
We want to change this before the release to anonymous users.
== User story
No impact on end user. Improves developer experience and maintainability long term. Also aligns code with product naming convention
### AC
[] Rename ClientPreference Feature flags and classes
[] Rename ClientPreferencePinned Feature flags and classes
[] Rename vector-client-prefs-pinned to vector-appearance-pinned
### QA steps
On beta cluster (check the environment is ready with a developer before starting)
* As anonymous user (using ?vectorappearance=1), check that you can pin the appearances menu. ON page refresh it should remain in the previous state you left it.
* Unpin the menu and refresh.
* As logged in user, check that you can pin the appearances menu. ON page refresh it should remain in the previous state you left it.
* Refresh and confirm it is still pinned.
== Communication criteria - does this need an announcement or discussion?
no