Support for experimental MSC4286 to not render external payment details

[hughns]

Ref: matrix-org/matrix-spec-proposals#4286

Before	After

In the above example the formatted_body of the event looks like this:

Thanks for subscribing!<span data-msc4286-external-payment-details> You can manage your subscription and view your payment history <a href="https://account.example.com/account/plan">here</a> at any time</span>

Pull Request Checklist

• I read the contributing guide
• UI change has been tested on both light and dark themes, in portrait and landscape orientations and on iPhone and iPad simulators
• Accessibility has been taken into account.

• Pull request is based on the develop branch

• Pull request contains a changelog file in ./changelog.d
• You've made a self review of your PR
• Pull request includes screenshots or videos of UI changes
• Pull request includes a sign off

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 15.56%. Comparing base (478d4f7) to head (5a769d6).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7927      +/-   ##
===========================================
+ Coverage    14.40%   15.56%   +1.16%     
===========================================
  Files         1812     1812              
  Lines       173783   173783              
  Branches     67244    67244              
===========================================
+ Hits         25028    27050    +2022     
+ Misses      148105   146083    -2022     
  Partials       650      650              

Flag	Coverage Δ
uitests	60.16% <ø> (+9.52%)	⬆️

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[hughns]

I'm not sure what the problem with CI is.