feat: add fastly provider

[btkostner]

This adds a fastly image optimization provider.

• I tried to get the size operator matched up as much as I could, but they only have three options.
• I added a fastly url, but because it's a demo url, the only available image to test on is /image.jpg

[codecov-commenter]

Codecov Report

Merging #15 into master will increase coverage by 1.62%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
+ Coverage   53.16%   54.78%   +1.62%     
==========================================
  Files          15       17       +2     
  Lines         348      376      +28     
  Branches      103      113      +10     
==========================================
+ Hits          185      206      +21     
- Misses        163      170       +7     

Impacted Files	Coverage Δ
src/providers/fastly/runtime.ts	73.07% <73.07%> (ø)
src/providers/fastly/index.ts	100.00% <100.00%> (ø)

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[farnabaz]

Great, Thanks 👍