contrib/google.golang.org/api: change gen_endpoints script to generate a json file

[rarguelloF]

What does this PR do?

contrib/google.golang.org/api: change gen_endpoints script to generate a json file instead of a Go file.

Motivation

Improve memory footprint of the package and fix CI issues for the CI job Testing outlier google.golang.org/api like this:

Run go get google.golang.org/api@v0.121.0 # version used to generate code
Error: Process completed with exit code 143.

Running go test -v -toolexec '/usr/bin/time -l' ./contrib/google.golang.org/api/...

Before PR (650MB):

# gopkg.in/DataDog/dd-trace-go.v1/contrib/google.golang.org/api [gopkg.in/DataDog/dd-trace-go.v1/contrib/google.golang.org/api.test]
        2.25 real         2.46 user         0.15 sys
           662470656  maximum resident set size
                   0  average shared memory size
                   0  average unshared data size
                   0  average unshared stack size
               40668  page reclaims
                  21  page faults
                   0  swaps
                   0  block input operations
                   0  block output operations
                   0  messages sent
                   0  messages received
                 289  signals received
                  47  voluntary context switches
                3171  involuntary context switches
         35238301384  instructions retired
          7896108868  cycles elapsed
           651397376  peak memory footprint

After PR (3.2GB):

# gopkg.in/DataDog/dd-trace-go.v1/contrib/google.golang.org/api [gopkg.in/DataDog/dd-trace-go.v1/contrib/google.golang.org/api.test]
       14.01 real        15.01 user         0.59 sys
          3266461696  maximum resident set size
                   0  average shared memory size
                   0  average unshared data size
                   0  average unshared stack size
              199696  page reclaims
                   0  page faults
                   0  swaps
                   0  block input operations
                   0  block output operations
                   0  messages sent
                   0  messages received
                1837  signals received
                 173  voluntary context switches
               11076  involuntary context switches
        233336926892  instructions retired
         48981875346  cycles elapsed
          3255491712  peak memory footprint # 3,2GB

With this PR (81MB):

# gopkg.in/DataDog/dd-trace-go.v1/contrib/google.golang.org/api.test
        0.74 real         0.38 user         0.08 sys
           277987328  maximum resident set size
                   0  average shared memory size
                   0  average unshared data size
                   0  average unshared stack size
               10959  page reclaims
                7571  page faults
                   0  swaps
                   0  block input operations
                   0  block output operations
                   0  messages sent
                   0  messages received
                 114  signals received
                 256  voluntary context switches
                4573  involuntary context switches
          4873847759  instructions retired
          1476368924  cycles elapsed
            81659328  peak memory footprint

Describe how to test/QA your changes

Reviewer's Checklist

• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Comparing candidate commit d92356d in PR branch rarguelloF/improve-memory-contrib-google-api with baseline commit fbd37ea in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.