build: Add dependabot config file

By telling it there are go.mod files in example/*, hopefully this will
limit the need for commits where we run `go mod tidy` ourselves.

Signed-off-by: Christophe Fergeau <[email protected]>

Author: cfergeau

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+- package-ecosystem: gomod
+  directory: "/"
+- package-ecosystem: gomod
+  directory: "/example/gui-linux"
+- package-ecosystem: gomod
+  directory: "/example/linux"
+- package-ecosystem: gomod
+  directory: "/example/macos"
+- package-ecosystem: github-actions
+  directory: "/"