feat(providers): add provider.auto-stop-on-startup argument (#346)

This feature adds the capability to stop unregistered running instances upon startup.

Previously, you had to stop running instances manually or issue an initial request that will shut down instances afterwards.

With this change, all discovered instances will be shutdown. They need to be registered using labels. E.g.: sablier.enable=true

Fixes #153

plugins/proxywasm/e2e/envoy/docker/compose.yaml

@@ -19,9 +19,15 @@ services:
 
   whoami:
     image: containous/whoami:v1.5.0
+    labels:
+      - sablier.enable=true
+      - sablier.group=E2E
 
   nginx:
     image: nginx:1.27.0
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost"]
-      interval: 5s
+      interval: 5s
+    labels:
+      - sablier.enable=true
+      - sablier.group=E2E