[Infra] Update Dockerfiles with dependabot (#6315)

Author: martincostello

.github/dependabot.yml

@@ -6,6 +6,34 @@ updates:
       interval: "daily"
     labels:
       - "infra"
+  - package-ecosystem: "docker"
+    directory: "/examples/MicroserviceExample/WebApi"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    labels:
+      - "infra"
+  - package-ecosystem: "docker"
+    directory: "examples/MicroserviceExample/WorkerService"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    labels:
+      - "infra"
+  - package-ecosystem: "docker"
+    directory: "test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/IntegrationTest"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    labels:
+      - "infra"
+  - package-ecosystem: "docker"
+    directory: "test/OpenTelemetry.Instrumentation.W3cTraceContext.Tests"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    labels:
+      - "infra"
   - package-ecosystem: "dotnet-sdk"
     directory: "/"
     schedule: