Improve local user experience for User Credentials

[TimurSadykov]

This is part of the bigger work go/simplified-local-adc

User Credentials are now recommended for local development per go/mitigating-cloud-auth-risk

However, some errors and warnings still refer to service accounts (see section 1.2 of the go/simplified-local-adc):

1. When user does not have credential setup, we do not recommend setting up service account, rather we redirect to a new ADC setup page.
2. (if applicable) We show warning about user credentials only if production environment is detected
   Reference Java fix: fix: improve errors and warnings related to ADC google-auth-library-java#1172

[danielbankhead]

Today, we don't offer suggestions in the code suggesting service accounts or not (in docs, comments, or error messages). Here's how the missing ADC message looks like today:

google-auth-library-nodejs/src/auth/googleauth.ts

Lines 367 to 370 in 85f2c93

	// We failed to find the default credentials. Bail out with an error.
	throw new Error(
	'Could not load the default credentials. Browse to https://cloud.google.com/docs/authentication/getting-started for more information.'
	);

As for the second case:

• we've previously introduced this functionality in fix: Warn when using user credentials from the Cloud SDK #399
• updated in fix: deprecate the getDefaultProjectId method #402
• then ultimately reverted in fix: do not warn for SDK creds #905

I'm happy to revert #905 if the telemetry determines this provides a better user experience.

Let me know if anything else, closing for now.