(chore) Add dependabot config to keep tooling up to date. (open-telemetry#1346)

Co-authored-by: Armin Ruech <7052238+arminru@users.noreply.github.com>

Author: jsuereth

.github/dependabot.yml

@@ -0,0 +1,20 @@
+version: 2
+updates:
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+  - package-ecosystem: "github-actions"
+    directory: ".github"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+  - package-ecosystem: "gomod"
+    directory: "internal/tools"
+    schedule:
+      interval: "daily"
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "daily"