Option for variable frame rates to download as GIF option

[rishabhshuklax]

Fixes #743

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[codecov]

Codecov Report

Merging #1611 into main will increase coverage by 10.29%.
The diff coverage is 63.90%.

@@             Coverage Diff             @@
##             main    #1611       +/-   ##
===========================================
+ Coverage   55.11%   65.41%   +10.29%     
===========================================
  Files         117      132       +15     
  Lines        2344     2741      +397     
  Branches      360      438       +78     
===========================================
+ Hits         1292     1793      +501     
+ Misses       1052      948      -104     

Impacted Files	Coverage Δ
examples/lib/scopeQuery.js	18.51% <ø> (ø)
src/Modules.js	100.00% <ø> (ø)
src/modules/WebglDistort/Module.js	2.29% <0.00%> (ø)
src/ui/SetInputStep.js	12.90% <0.00%> (-1.39%)	⬇️
src/modules/ColorHalftone/Module.js	3.63% <3.63%> (ø)
examples/lib/defaultHtmlStepUi.js	11.35% <4.08%> (-0.85%)	⬇️
examples/lib/intermediateHtmlStepUi.js	11.11% <5.55%> (+0.94%)	⬆️
examples/lib/insertPreview.js	13.15% <20.00%> (-0.36%)	⬇️
src/util/getImageDimensions.js	20.00% <20.00%> (ø)
src/util/isGif.js	20.00% <20.00%> (ø)
... and 100 more

[rishabhshuklax]

@publiclab/is-reviewers please review this

[gitpod-io]

[harshkhandeparkar]

1. The frame duration unit is not shown
2. We should no allow any frame rate (-ve or too low etc)

[harshkhandeparkar]

1. The frame duration unit is not shown
2. We should no allow any frame rate (-ve or too low etc)

This could be merged if this is not a problem.