fix(gateway): return HTTP 500 on namesys.ErrResolveFailed

[hacdias]

Fixes ipfs/kubo#9514.

There's a catch here. AFAIK, there is no good way of distinguishing between a non-existing DNSLink entry and an IPNS key that cannot be resolved. With this PR, both return 500 Internal Server Error, as both return namesys.ErrResolveFailed as error. What do you think @lidel? If we want to treat both errors the same way, I think it's good to go. Otherwise, we may need further changes in the namesys package.

Sharness tests will fail here. See ipfs/kubo#9589.

[codecov]

Codecov Report

Merging #150 (77fb194) into main (c394290) will increase coverage by 0.21%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
+ Coverage   29.19%   29.41%   +0.21%     
==========================================
  Files          96       99       +3     
  Lines       11018    11093      +75     
==========================================
+ Hits         3217     3263      +46     
- Misses       7448     7472      +24     
- Partials      353      358       +5     

Impacted Files	Coverage Δ
gateway/handler.go	62.75% <100.00%> (+0.71%)	⬆️
gateway/handler_unixfs__redirects.go	38.79% <0.00%> (-0.55%)	⬇️
files/is_hidden_windows.go	82.35% <0.00%> (ø)
tar/sanitize_windows.go	41.66% <0.00%> (ø)
files/filewriter_windows.go	100.00% <0.00%> (ø)

[hacdias]

@lidel this would be easier to rebase once #156 is merged.

[lidel]

#156 Is merged, feel free to rebase and move tests from ipfs/kubo#9589 to this PR

[hacdias]

@lidel sharness will also fail here, as there is a single sharness test that checks the status code for this cases. See ipfs/kubo#9589 for Kubo PR.