feat: add BigQueryJob library

[scotthart]

As we need to keep bigquery_job separate from the existing bigquery target to avoid introducing REST dependencies, this required some massaging of our ci builds and generated inputs into those builds.

This PR is split into several commits to group related changes for easier reviewing.

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This change is 

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 33.19328% with 318 lines in your changes missing coverage. Please review.

Project coverage is 93.44%. Comparing base (6505814) to head (5d79418).

Files	Patch %	Lines
...gquery/job/v2/internal/job_rest_connection_impl.cc	7.31%	76 Missing :warning:
...le/cloud/bigquery/job/v2/internal/job_rest_stub.cc	5.79%	65 Missing :warning:
...bigquery/job/v2/internal/job_tracing_connection.cc	6.66%	42 Missing :warning:
...uery/job/v2/internal/job_rest_logging_decorator.cc	15.15%	28 Missing :warning:
google/cloud/bigquery/job/v2/job_client.cc	17.64%	28 Missing :warning:
...ery/job/v2/internal/job_rest_metadata_decorator.cc	21.87%	25 Missing :warning:
...gquery/job/v2/job_connection_idempotency_policy.cc	15.78%	16 Missing :warning:
google/cloud/bigquery/job/v2/job_connection.cc	6.66%	14 Missing :warning:
google/cloud/bigquery/job/v2/job_connection.h	58.33%	10 Missing :warning:
...igquery/job/v2/internal/job_rest_connection_impl.h	20.00%	8 Missing :warning:
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14403      +/-   ##
==========================================
- Coverage   93.58%   93.44%   -0.14%     
==========================================
  Files        2313     2332      +19     
  Lines      206885   207361     +476     
==========================================
+ Hits       193617   193776     +159     
- Misses      13268    13585     +317     

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[snippet-bot[bot]]

Here is the summary of possible violations 😱

There is a possible violation for not having product prefix.

• google/cloud/bigquery/quickstart/quickstart_job.cc:15, tag bigqueryjob_quickstart

The end of the violation section. All the stuff below is FYI purposes only.

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Here is the summary of changes.

You are about to add 1 region tag.

• google/cloud/bigquery/quickstart/quickstart_job.cc:15, tag bigqueryjob_quickstart

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