gateway: implement IPIP-0445 (skip-raw-blocks option)

[Jorropo]

See https://github.com/ipfs/specs/pull/445

[Jorropo]

Need tests merged and changelog.

[codecov[bot]]

Codecov Report

Merging #502 (f7bb4b3) into main (9c22812) will decrease coverage by 0.09%. The diff coverage is 32.14%.

@@            Coverage Diff             @@
##             main     #502      +/-   ##
==========================================
- Coverage   65.66%   65.58%   -0.09%     
==========================================
  Files         207      207              
  Lines       25604    25656      +52     
==========================================
+ Hits        16814    16827      +13     
- Misses       7317     7353      +36     
- Partials     1473     1476       +3     

Files	Coverage Δ
gateway/blocks_backend.go	43.24% <59.09%> (+0.52%)	:arrow_up:
gateway/handler_car.go	74.74% <9.09%> (-3.87%)	:arrow_down:
gateway/gateway.go	74.66% <17.39%> (-10.38%)	:arrow_down:

... and 12 files with indirect coverage changes