Make cookie domain settable via config

[oalders]

Right now auth seem to be using both fastapi.metacpan.org and api.metacpan.org

Try to have a more robust way of handling this.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.65%. Comparing base (12bcd70) to head (1522bf2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1488      +/-   ##
==========================================
+ Coverage   63.55%   63.65%   +0.09%     
==========================================
  Files         137      137              
  Lines        4467     4468       +1     
  Branches      670      671       +1     
==========================================
+ Hits         2839     2844       +5     
+ Misses       1374     1370       -4     
  Partials      254      254              

Files with missing lines	Coverage Δ
lib/MetaCPAN/Server/Controller/Login.pm	42.42% <100.00%> (+8.04%)	⬆️

... and 1 file with indirect coverage changes

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