`ECONNRESET` errors with using REST transport in GCF

[alexander-fenster]

As reported in https://github.com/googleapis/nodejs-firestore/issues/1943, @google-cloud/firestore used in GCF in REST mode {preferRest: true}, which translates to {fallback: 'rest'}, often results in ECONNRESET error. We need to investigate what might be going on.

[danielbankhead]

It appears we have 2 networking libraries in the fallback: 'rest' path:

• google-auth-library
• node-fetch

google-auth-library currently has retries for the ECONNRESET concern, however the node-fetch path does not. Perhaps a way forward is to swap node-fetch with gaxios with a retry configuration, here:

https://github.com/googleapis/gax-nodejs/blob/d140b9c5c38a3e0c4bdc6c138796936cf030c1bf/gax/src/fallbackServiceStub.ts#L73-L75