When there is an official solution for pino to GCP logging, use that instead of own fix

[haphut]

A currently open issue for Google: googleapis/nodejs-logging#875 Google provides libraries for logging into GCP using bunyan (https://github.com/googleapis/nodejs-logging-bunyan) or winston but not yet for pino. It seems that e.g. logging objects is not as easy as just changing pino levels to GCP severity.

Either Google provides a library for pino (best case), pino builds more internal tooling for GCP or we will keep using our workaround.

(Original issue for pino: pinojs/pino#726)

(There also exists https://github.com/guillenotfound/pino-gcp-logger but it is not the cleanest TypeScript, it's made by one individual, looks unmaintained (but should probably not need maintenance) and is one more dependency for one-file solution.)