Add support for Cloud Run environment variables.

The Python debug agent will now:
Use K_SERVICE to populate the service context (if available).
Use K_REVISION to populate the version context (if available).

PiperOrigin-RevId: 235231863
Change-Id: Ia0cba9465b2b0b44f86411ae5692d41c184e353c

Author: mctavish

src/googleclouddebugger/gcp_hub_client.py

@@ -56,8 +56,10 @@
 # a map is optional environment variable that can be used to set the flag
 # (flags still take precedence).
 _DEBUGGEE_LABELS = {
-    labels.Debuggee.MODULE: ['GAE_SERVICE', 'GAE_MODULE_NAME'],
-    labels.Debuggee.VERSION: ['GAE_VERSION', 'GAE_MODULE_VERSION'],
+    labels.Debuggee.MODULE: ['GAE_SERVICE', 'GAE_MODULE_NAME', 'K_SERVICE'],
+    labels.Debuggee.VERSION: [
+        'GAE_VERSION', 'GAE_MODULE_VERSION', 'K_REVISION'
+    ],
     labels.Debuggee.MINOR_VERSION: ['GAE_DEPLOYMENT_ID', 'GAE_MINOR_VERSION']
 }