Slash command to manually discard outbound session

[Anderas]

This is equivalent to the /discardsession command used in the web client

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[github-actions]

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[pixlwave]

LGTM 😎

[codecov-commenter]

Codecov Report

Merging #6668 (9b0b579) into develop (b0dd477) will decrease coverage by 0.05%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #6668      +/-   ##
===========================================
- Coverage     6.26%    6.21%   -0.06%     
===========================================
  Files         1475     1475              
  Lines       155168   155177       +9     
  Branches     62265    62264       -1     
===========================================
- Hits          9718     9639      -79     
- Misses      145045   145135      +90     
+ Partials       405      403       -2     

Impacted Files	Coverage Δ
Riot/Modules/Room/MXKRoomViewController.m	0.00% <0.00%> (ø)
Config/CommonConfiguration.swift	85.71% <0.00%> (-5.20%)	⬇️
Riot/Managers/Call/CallPresenter.swift	1.08% <0.00%> (-5.14%)	⬇️
...rs/EncryptionKeyManager/EncryptionKeyManager.swift	35.41% <0.00%> (-4.17%)	⬇️
...xKit/Controllers/MXKAuthenticationViewController.m	17.04% <0.00%> (-1.92%)	⬇️
Riot/Modules/Application/LegacyAppDelegate.m	13.37% <0.00%> (-0.34%)	⬇️
...ojiPicker/Data/EmojiMart/EmojiItem+EmojiMart.swift	95.65% <0.00%> (+0.30%)	⬆️
...dules/Room/EmojiPicker/Data/Store/EmojiStore.swift	88.37% <0.00%> (+4.65%)	⬆️

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