Replace httpretty

[ocefpaf]

httpretty seems to be abandoned and some of its deprecation warnings will make it unsuable soon. See gabrielfalcao/HTTPretty#482

I'm replace it with mocket, which seems to have a 1-1 correspondence and seems to be well maintained.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.17%. Comparing base (37ef414) to head (5c56994).
Report is 5 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1125   +/-   ##
========================================
  Coverage    82.17%   82.17%           
========================================
  Files           25       25           
  Lines         5206     5206           
  Branches      1162     1162           
========================================
  Hits          4278     4278           
  Misses         627      627           
  Partials       301      301           

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[ocefpaf]

The docs failure is unrelated to this PR:

(             faq: line   24) broken    https://standards.sensors.ioos.us/erddap/tabledap/morro-bay-bs1-met.html - 502 Server Error: Bad Gateway for url

If that link is not back online we will need to remove/find an alternative to it