feat(MediaSourceDesc): add source name

[paweldomas]

The source names are to be used for the multiple streams per endpoint support.

[codecov]

Codecov Report

Merging #374 (a6e6b9f) into master (510c491) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #374      +/-   ##
============================================
+ Coverage     43.86%   43.87%   +0.01%     
- Complexity      551      552       +1     
============================================
  Files           144      144              
  Lines          5583     5584       +1     
  Branches        773      773              
============================================
+ Hits           2449     2450       +1     
  Misses         2829     2829              
  Partials        305      305              

Impacted Files	Coverage Δ
src/main/kotlin/org/jitsi/nlj/MediaSourceDesc.kt	52.17% <100.00%> (+1.06%)	⬆️

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