Expose sliding sync proxy URL on the server selection screen

[stefanceriu]

This PR will:

• move the sliding sync server url to the user defaults
• expose it on the server selection screen
• make the app more resilient to slidinc sync configuration errors. Instead of throwing fatal errors it will allow the app to start and show the home screen but will always stay in the skeletons view. The user can choose to log out and change the server settings.

[github-actions]

	Warnings
⚠️	Some of the commits are missing ticket numbers. Please consinder using them for better tracking.

Generated by 🚫 Danger Swift against e07ee1e

[codecov]

Codecov Report

Base: 33.77% // Head: 33.77% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (119933e) compared to base (2fd0491).
Patch coverage: 60.00% of modified lines in pull request are covered.

❗ Current head 119933e differs from pull request most recent head e07ee1e. Consider uploading reports for the commit e07ee1e to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #320   +/-   ##
========================================
  Coverage    33.77%   33.77%           
========================================
  Files          252      253    +1     
  Lines        16514    16594   +80     
  Branches      8917     9000   +83     
========================================
+ Hits          5577     5605   +28     
- Misses       10774    10831   +57     
+ Partials       163      158    -5     

Flag	Coverage Δ
unittests	13.62% <26.66%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
ElementX/Sources/Application/BuildSettings.swift	0.00% <0.00%> (ø)
...cation/ServerSelection/ServerSelectionModels.swift	100.00% <ø> (ø)
ElementX/Sources/Services/Client/ClientProxy.swift	0.00% <0.00%> (ø)
...urces/Screens/HomeScreen/HomeScreenViewModel.swift	58.12% <71.87%> (+2.72%)	⬆️
ElementX/Sources/Other/ElementSettings.swift	93.33% <100.00%> (-6.67%)	⬇️
...ion/ServerSelection/ServerSelectionViewModel.swift	86.84% <100.00%> (-5.76%)	⬇️
...n/ServerSelection/View/ServerSelectionScreen.swift	66.66% <100.00%> (-11.91%)	⬇️
...entX/Sources/Services/Client/MockClientProxy.swift	20.58% <100.00%> (ø)
... and 3 more

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication