Define log domain

[Peter Uithoven]

Problem

It's currently quite hard to debug wingpanel indicators as there are many indicators that add log messages. There isn't a good way to filter this to a specific indicator.

Proposal

We could define log domains:
https://developer.gnome.org/glib/stable/glib-Message-Logging.html#log-domains

This enables filtering log messages using G_MESSAGES_DEBUG, to do do something like the following to only get the logs from a specific indicator and the wingpanel:

G_MESSAGES_DEBUG=io.elementary.wingpanel.bluetooth wingpanel

Prior Art

We've added this to the bluetooth indicator
elementary/wingpanel-indicator-bluetooth#81