Missing Feature to actually (un-) pin messages and show messages which are pinned

### Your use case

Our company is working on a tailored version of the client for one of our customers.
One thing which was missing was the function of showing pinned messages and to (un-)pin messages.
I have worked on a solution, which could be found here:

https://heptapod.host/intevation/fac/ios-client/-/tree/pinbutton

I have to admit not having written any _Objective-C_ before nor having done _iOS_-development before.
Therefore the solution written has to be taken with a (big) grain of salt.

And while being aware of the quality not being "production ready" I offer this not as a pull request but share the link as a source of _inspiration_. Hopefully someone finds it useful.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_