Add configurable launcher gallery

[philippjfr]

Previously it was only possible to configure a single launcher via the CLI --launcher argument. This did not allow a lot of configurability and often you want to offer users multiple options for launching/deploying/exporting. This PR adds a Launcher gallery which can be configured just like any other components by adding yaml specifications to the ./components/launchers/ directory.

[codecov-commenter]

Codecov Report

Merging #270 (446dcbb) into master (93d1081) will decrease coverage by 0.33%.
The diff coverage is 41.81%.

@@            Coverage Diff             @@
##           master     #270      +/-   ##
==========================================
- Coverage   65.43%   65.10%   -0.34%     
==========================================
  Files          57       57              
  Lines        5511     5559      +48     
==========================================
+ Hits         3606     3619      +13     
- Misses       1905     1940      +35     

Impacted Files	Coverage Δ
lumen/ui/base.py	34.72% <ø> (-4.17%)	⬇️
lumen/ui/main.py	31.81% <0.00%> (-1.52%)	⬇️
lumen/ui/sources.py	50.45% <ø> (ø)
lumen/ui/state.py	75.60% <ø> (-0.59%)	⬇️
lumen/ui/builder.py	27.43% <25.00%> (-1.14%)	⬇️
lumen/ui/gallery.py	44.28% <33.33%> (-0.50%)	⬇️
lumen/ui/launcher.py	50.00% <44.68%> (-15.72%)	⬇️

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[github-actions]

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