Unbreak the build (fix #586 #597)

[sloshy]

Fixes the build by solving two separate issues:

1. Ignores a failing test that was deemed safe to ignore (Ignore the reviewers test #586)
2. Removes the Auth.newAuth functionality as logging in with a username/password is now officially discontinued (Remove Auth.newAuth as it has been discontinued #597)

This includes the requisite changes to documentation as well as a quick tweak to the .gitignore to properly filter out metals.sbt in all directories.

[sloshy]

Marked WIP as there seems to be another test failing. Not sure if it should hold up the fix.

[codecov]

Codecov Report

Merging #595 (09a3b4d) into master (fbb265a) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #595      +/-   ##
==========================================
- Coverage   90.29%   90.18%   -0.12%     
==========================================
  Files          25       25              
  Lines         608      611       +3     
  Branches        3        1       -2     
==========================================
+ Hits          549      551       +2     
- Misses         59       60       +1     

Impacted Files	Coverage Δ
...s/src/main/scala/github4s/domain/PullRequest.scala	100.00% <ø> (ø)
.../scala/github4s/interpreters/AuthInterpreter.scala	100.00% <ø> (ø)
github4s/src/main/scala/github4s/Decoders.scala	91.91% <100.00%> (ø)
github4s/src/main/scala/github4s/Encoders.scala	96.77% <100.00%> (ø)
...ithub4s/interpreters/PullRequestsInterpreter.scala	100.00% <100.00%> (ø)
...ub4s/src/main/scala/github4s/http/HttpClient.scala	92.68% <0.00%> (-2.44%)	⬇️

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[sloshy]

Ok, after a lot of trial and error (Metals was not reporting any of the errors that github found) I've turned this PR into fixing the build entirely, and edited the description to match. Code coverage is slightly down but I don't think that's an issue since it's a result of one test being removed (as the feature was removed) and then one test being ignored (as the issue states).

[BenFradet]

👍