dependabot: use directories and use docker ecosystem (#276)

Author: v1v

.github/dependabot.yml

@@ -1,5 +1,12 @@
 ---
 version: 2
+registries:
+  docker-elastic:
+    type: docker-registry
+    url: https://docker.elastic.co
+    username: ${{secrets.ELASTIC_DOCKER_USERNAME}}
+    password: ${{secrets.ELASTIC_DOCKER_PASSWORD}}
+
 updates:
   # Enable version updates for python
   - package-ecosystem: "pip"
@@ -12,9 +19,10 @@ updates:
     reviewers:
       - "elastic/apm-agent-python"
 
-  # GitHub actions
   - package-ecosystem: "github-actions"
-    directory: "/"
+    directories:
+      - '/'
+      - '/.github/actions/*'
     reviewers:
       - "elastic/observablt-ci"
     schedule:
@@ -26,16 +34,11 @@ updates:
         patterns:
           - "*"
 
-  # GitHub composite actions
-  - package-ecosystem: "github-actions"
-    directory: "/.github/actions/env-install"
+  - package-ecosystem: "docker"
+    directories:
+      - '/'
     reviewers:
-      - "elastic/observablt-ci"
+      - "elastic/apm-agent-python"
+    registries: "*"
     schedule:
-      interval: "weekly"
-      day: "sunday"
-      time: "22:00"
-    groups:
-      github-actions:
-        patterns:
-          - "*"
+      interval: "daily"