Use SVG icons for welcome module

[ekdahl]

Adds default SVG icons that is currently still overridden by supplied themes.
There are probably better ways to do this. Feedback welcome.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 35.26%. Comparing base (e636546) to head (ce174bf).

Files with missing lines	Patch %	Lines
app/Module/UserWelcomeModule.php	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5087      +/-   ##
============================================
- Coverage     35.26%   35.26%   -0.01%     
  Complexity    11413    11413              
============================================
  Files          1181     1181              
  Lines         47917    47920       +3     
============================================
  Hits          16900    16900              
- Misses        31017    31020       +3     

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