feat(bigquery/admin/v2): generate library

[coryan]

Generate the "admin" library. This is basically the bigquery/v2 library with
some omissions.

I think we will want to include the Query() and GetQueryResults() RPCs in a
hand-crafted library, and probably using the BigQuery Storage APIs as the
underlying implementation. If I am wrong, we can always add these methods back.

Fixes #829

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.19%. Comparing base (a9c0c0c) to head (c4d565e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1540   +/-   ##
=======================================
  Coverage   95.19%   95.19%           
=======================================
  Files          39       39           
  Lines        1603     1603           
=======================================
  Hits         1526     1526           
  Misses         77       77           

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[dbolduc]

Approved, but check the not-for-publication = 'true' bit. Seems wrong to me, but maybe I don't know the plan.

[dbolduc]

I am iffy, but ok with making up an admin directory when it doesn't exist...

I am guessing the eventual veneer will be google-cloud-bigquery and you are trying to avoid confusion between that and google-cloud-bigquery-v2

[coryan]

I am iffy, but ok with making up an admin directory when it doesn't exist...

The directory does not matter. We can move packages around, remember? Only the package name matters. I picked the directory to match the package name.

I am guessing the eventual veneer will be google-cloud-bigquery and you are trying to avoid confusion between that and google-cloud-bigquery-v2

google-cloud-bigquery (in the src/bigquery directory) seems likely. I renamed the package because it is a selection from google-cloud-bigquery-v2, but now that you ask, I am not sure... Let me ponder this a bit.