Need to reenable quickstart tests on 3 libraries that need SA key credentials

[sofisl]

These libraries need an actual SA key credential saved to the GOOGLE_CLOUD_APPLICATIONS_CREDENTIAL variable, but this is not supported with our current Cloud Build triggers. We need to create a new trigger that only runs for these select libraries and fills this env variable in with the value from a secret. These are the libraries that need sample tests reenabled:

[ ] #3600
[ ] #3564
[ ] #3562