fix: nodejs build_gen uses grpc_service_config

[noahdietz]

fix: nodejs build_gen uses grpc_service_config

fix: ignore grpc_service_config unless using gapic_v2

fix: use None instead of "" when grpc_service_config is not present

cc: @alexander-fenster

[codecov]

Codecov Report

Merging #3206 into master will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #3206      +/-   ##
============================================
- Coverage     87.13%   87.12%   -0.01%     
  Complexity     6077     6077              
============================================
  Files           494      494              
  Lines         24051    24052       +1     
  Branches       2612     2613       +1     
============================================
  Hits          20956    20956              
- Misses         2233     2234       +1     
  Partials        862      862              

Impacted Files	Coverage Δ	Complexity Δ
...om/google/api/codegen/gapic/GapicGeneratorApp.java	54.09% <0.00%> (-0.45%)	6.00 <0.00> (ø)

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[vam-google]

LGTM, though nodejs has already migrated to microgenerator completely (including bazel presubmits)

[noahdietz]

though nodejs has already migrated to microgenerator completely (including bazel presubmits)

build_gen still generates the gapic_yaml attribute in nodejs_gapic_library, which is unused because the implementation of that rule is provided via gapic-generator-typescript. This fixes that.