Refactor the control flow for manifests and blobs.

[mattmoor]

I noticed that these functions were giant switch statements without the switch, they should also be using http.MethodFoo instead of constants.

[codecov-commenter]

Codecov Report

Merging #1157 (86dfaa8) into main (b0e827a) will decrease coverage by 0.18%.
The diff coverage is 83.90%.

@@            Coverage Diff             @@
##             main    #1157      +/-   ##
==========================================
- Coverage   75.40%   75.22%   -0.19%     
==========================================
  Files         108      108              
  Lines        7824     7850      +26     
==========================================
+ Hits         5900     5905       +5     
- Misses       1361     1379      +18     
- Partials      563      566       +3     

Impacted Files	Coverage Δ
pkg/registry/blobs.go	88.52% <81.57%> (-11.48%)	⬇️
pkg/registry/manifest.go	94.14% <100.00%> (+0.04%)	⬆️

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[imjasonh]

Thanks! 🎉