feat: ad-hoc, targeted debug logging

[feywind]

This feature will add the ability to selectively enable "printf debugging" output for diagnostic introspection. This uses the new standard Google ad-hoc debug logging infrastructure introduced a few months back.

Samples:

GOOGLE_SDK_NODE_LOGGING=pubsub:*

All hand-written logic on top of the auto-generated RPCs.

GOOGLE_SDK_NODE_LOGGING=pubsub*

All logging related to Pub/Sub (including the RPCs).

GOOGLE_SDK_NODE_LOGGING=*

All logging, including things like auth.

A fuller guide will be forthcoming.

[sofisl]

same general comment about private elements

[sofisl]

since you're adding a param, wouldn't you need to add a default value to make it backwards-compatible or make it optional?

[feywind]

These two are internal/private methods, so they shouldn't need a default. I'm trying to make sure that everything that calls them gets updated for the logging, but at this point I guess it would be okay to add a default? Users definitely shouldn't be calling these directly, so I am also fine with just leaving it as-is.

[feywind]

Also, re: private methods, this library is pretty old and wasn't built to use them, so it would be pretty painful to add it now, imo. I'll definitely think about that going forward, but e.g. a lot of the unit tests assume that innards are accessible for mocking. I'd like to find a better way to do the unit tests too, but there are over 900 of them now 😅

[feywind]

I went ahead and made those optional parameter changes.