Enable dependabot for sigv4

Also update the sigv4 go.mod with dependabot.

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

.github/dependabot.yml

@@ -4,3 +4,7 @@ updates:
     directory: "/"
     schedule:
       interval: monthly
+  - package-ecosystem: "gomod"
+    directory: "/sigv4"
+    schedule:
+      interval: monthly