Add datasource.NewBigqueryClient

[k1LoW]

No description provided.

[codecov]

Codecov Report

Merging #206 into master will decrease coverage by 0.90%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #206      +/-   ##
==========================================
- Coverage   67.29%   66.39%   -0.91%     
==========================================
  Files          20       20              
  Lines        3428     3431       +3     
==========================================
- Hits         2307     2278      -29     
- Misses        884      921      +37     
+ Partials      237      232       -5     

Impacted Files	Coverage Δ
datasource/datasource.go	21.45% <0.00%> (-12.89%)	⬇️

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