Add drm collector to start having metrics from AMD GPUs (#190)

Even that not all servers have AMD GPUs the impact in terms of
performance for time of collecting metrics is not considerable.

src/charm.py

@@ -418,6 +418,7 @@ def _additional_integrations(self) -> Dict[str, Any]:
                 else "/var/lib/snapd/hostfs",
                 "enabled": True,
                 "enable_collectors": [
+                    "drm",
                     "logind",
                     "systemd",
                     "mountstats",