update GAClient to use 0.9.x google API

[wjordan]

This PR updates GAClient (a helper class used by the admin reports controller for some level-completion pages) to the >= 0.9.x google API, which was previously upgraded in #15995 causing this page to no longer work correctly.

I used #16132 as a reference for the Google API service migration, storing new JSON-format credentials in the CDO.ga_account secrets key (set via Chef cdo-secrets override_attribute on the baseline role, which gets propagated across all infrastructure instances).

Manually tested/verified locally with credentials provided via locals,yml using the following line of code (derived from the logic in the admincontroller which uses this class):

bundle exec ruby -r./deployment -r./dashboard/scripts/archive/ga_client/ga_client \
-e "puts GAClient.query_ga( \
  '2017-08-01', \
  '2017-08-02', \
  'ga:pagePath', \
  'ga:avgTimeOnPage', \
  'ga:pagePath=~^/s/|^/flappy/|^/hoc/' \
).rows"

/HOC/1
13.0
/flappy/1
[...etc...]

[tanyaparker]

Thank you thank you thank you!

[ashercodeorg]

LGTM!

[ashercodeorg]

nit: Pretty sure you don't need the to_s conversion.

[wjordan]

irb(main):001:0> 'ga:' + CDO.ga_profile_id
TypeError: no implicit conversion of Fixnum into String
        from (irb):1:in `+'
        from (irb):1
        from /usr/bin/irb:11:in `<main>'

[ashercodeorg]

Fascinating.

irb(main):003:0> 'ga:' + CDO.ga_profile_id
=> "ga:68074336"

[wjordan]

("ga:#{CDO.ga_profile_id}" is a valid alternative, because string-interpolation automatically adds #to_s to non-string objects)