chore: setup dependabot for new sub-modules (#1110)

Signed-off-by: Matthieu MOREL <[email protected]>

Author: mmorel-35

.github/dependabot.yml

@@ -17,6 +17,14 @@ updates:
     directory: /
     schedule:
       interval: weekly
+  - package-ecosystem: gomod
+    directory: /contrib
+    schedule:
+      interval: weekly
+  - package-ecosystem: gomod
+    directory: /envoy
+    schedule:
+      interval: weekly
   - package-ecosystem: docker
     directory: /examples/dyplomat
     schedule:
@@ -35,6 +43,10 @@ updates:
       - dependency-type: direct
     schedule:
       interval: weekly
+  - package-ecosystem: gomod
+    directory: /ratelimit
+    schedule:
+      interval: weekly
   - package-ecosystem: gomod
     directory: /xdsmatcher
     schedule: