feat: add debug logging support

[feywind]

Adds debug logging support for auth.

It's also waiting on this to finish:
googleapis/gax-nodejs#1669

This is a duplicate of another PR to make the GitHub bot macguffins go.

[d-goog]

Hello! With recent enhancements in the library we may be able to greatly streamline this PR by adding a listener here (thanks to the removal of Transporter):

• google-auth-library-nodejs/src/auth/authclient.ts

  Lines 325 to 345 in a511e56

  	static readonly DEFAULT_REQUEST_INTERCEPTOR: Parameters<
  	Gaxios['interceptors']['request']['add']
  	>[0] = {
  	resolved: async config => {
  	// Set `x-goog-api-client`, if not already set
  	if (!config.headers.has('x-goog-api-client')) {
  	const nodeVersion = process.version.replace(/^v/, '');
  	config.headers.set('x-goog-api-client', `gl-node/${nodeVersion}`);
  	}
  	// Set `User-Agent`
  	const userAgent = config.headers.get('User-Agent');
  	if (!userAgent) {
  	config.headers.set('User-Agent', USER_AGENT);
  	} else if (!userAgent.includes(`${PRODUCT_NAME}/`)) {
  	config.headers.set('User-Agent', `${userAgent} ${USER_AGENT}`);
  	}
  	return config;
  	},
  	};

Every auth request goes through this function. Let me know if you’d like to sync on this or have any questions.

[feywind]

@d-goog Ah, lovely. Thanks!

[d-goog]

Completely optional: Since these classes extend AuthClient we could use the class's setMethodName and avoid importing AuthClient.

Suggested change

	AuthClient.setMethodName(opts, 'fetchIdToken');
	UserRefreshClient.setMethodName(opts, 'fetchIdToken');

Here and in other places

[feywind]

Actually, after thinking about it, I'm not a super fan of static inheritance like that. I think it makes it more obscure what's actually being called. (Also, several of the other usages were not deriving from anything that had setMethodName so the usage was mixed.) I'm okay with it either way, but maybe leaning toward not changing it.