feat: implement and observe MSC4278 config value

[Velin92]

This PR

• Updates Ruma to use the improved MediaPreviewConfig event type that also supports a Default for the content type
• Implemented a way to observe the stable and unstable values of the event and return the used one accordingly, if no one is present the default will be used
• Set the value (will only use unstable type for now)

[codecov]

Codecov Report

Attention: Patch coverage is 64.70588% with 18 lines in your changes missing coverage. Please review.

Project coverage is 85.82%. Comparing base (ea4c9a4) to head (1c91e27).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/account.rs	62.50%	12 Missing ⚠️
crates/matrix-sdk/src/test_utils/mocks/mod.rs	68.42%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5040      +/-   ##
==========================================
- Coverage   85.85%   85.82%   -0.04%     
==========================================
  Files         325      325              
  Lines       35937    35988      +51     
==========================================
+ Hits        30855    30887      +32     
- Misses       5082     5101      +19     

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[poljar]

Looks mostly good, there are some missing docs here an there.

It would have been nice if this was spit out into separate commits. There are clear separation points. For example the extending of the mocking server could have been one commit, the functionality in the SDK a second one, and finally the bindings the third one.

But ok, it's not that big of a PR so it's still reviewable without this separation. Just something to keep in mind.

[poljar]

I see you have force pushed to implement the requested changes. Please refrain in the future from doing so, it makes the subsequent review rounds harder.

Our contributing guide explains the preferred review process: https://github.com/matrix-org/matrix-rust-sdk/blob/main/CONTRIBUTING.md#review-process.

[poljar]

There's still some docs missing and I just realized that there's going to be a small race.

Looks almost ready to be merged.

I know that I complained about force pushes, but now the CI is broken unless you rebase onto main.

So feel free to do that.

[poljar]

Thanks, looks good now.