feat(bindings): added APIs to get the media preview config from the store

[Velin92]

The reason behind this PR, is to extend #5040
While the observable value is very useful in the context of the main app, it may be problematic in the context of parallel processes that aim to aid the main app process, like for example the Notification Service Extension on iOS, which is treated as a different process, and has some very harsh memory contraints, and a limited lifetime, which would make the observable values not quite useful.

Also while we do have a get_media_preview_config_event_content that is used by the observable API, this sends a request to the server to check for the current account data value of such event, and in the context of the NSE which already waits for a sync, we probably do not want to slow it down with another request to the server (not mentioning that sending a request for each notification might be also problematic for the servers).
For the NSE scenario I think getting whatever is currently in the store would be fine.

[Velin92]

@poljar I wonder if we shouldn't actually use also in the observable API the currently stored value, instead of doing a request to the server... WDYT?

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.75%. Comparing base (d462683) to head (f8ae8fb).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/account.rs	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5062      +/-   ##
==========================================
- Coverage   85.81%   85.75%   -0.06%     
==========================================
  Files         325      325              
  Lines       35922    35932      +10     
==========================================
- Hits        30826    30815      -11     
- Misses       5096     5117      +21     

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[poljar]

@poljar I wonder if we shouldn't actually use also in the observable API the currently stored value, instead of doing a request to the server... WDYT?

As mentioned here: #5062 (comment). Yes we can do that.

[poljar]

Looks good, let's just rename the methods a bit.

[poljar]

Thanks, looking good.