impl(bigquery): support default project_id on ClientBuilder

[haphungw]

Add support for configuring a default GCP project_id on ClientBuilder, which is stored on the BigQuery client and automatically used as the billing project when running queries or attaching to jobs.

For #6198

[gemini-code-assist]

Code Review

This pull request adds support for configuring a default Google Cloud project ID on the BigQuery client using the builder pattern, which is then automatically applied to executed queries. The feedback identifies a compilation error in BigQuery::query where a &String is passed to a method expecting Into<String>, and suggests using .as_str() to resolve the trait bound issue.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.26%. Comparing base (2a8ee0c) to head (69e486f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6293   +/-   ##
=======================================
  Coverage   96.25%   96.26%           
=======================================
  Files         283      283           
  Lines       72936    72982   +46     
=======================================
+ Hits        70203    70253   +50     
+ Misses       2733     2729    -4     

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[alvarowolfx]

I think we can add a example section on the new with_project_id method.