feat(gw): add ipfs_http_gw_car_stream_fail_duration_seconds

[lidel]

This PR adds failure metrics to streaming response types (CAR and TAR)
to give us better visibility (histograms) into how long it takes for CAR to fail mid-stream.

Closes #288

[Jorropo]

<3

[codecov]

Codecov Report

Merging #312 (f6bf439) into main (fee5f6b) will decrease coverage by 0.02%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main     #312      +/-   ##
==========================================
- Coverage   48.12%   48.10%   -0.02%     
==========================================
  Files         279      279              
  Lines       33511    33526      +15     
==========================================
+ Hits        16127    16128       +1     
- Misses      15696    15707      +11     
- Partials     1688     1691       +3     

Impacted Files	Coverage Δ
gateway/handler.go	57.56% <ø> (ø)
gateway/handler_car.go	0.00% <0.00%> (ø)
gateway/handler_tar.go	0.00% <0.00%> (ø)
gateway/metrics.go	62.18% <100.00%> (+1.48%)	⬆️

... and 5 files with indirect coverage changes