Set up dependabot (#25)

To keep our dependencies up-to-date.
https://docs.github.com/en/code-security/dependabot/working-with-dependabot

Author: getkey

.github/dependabot.yml

@@ -0,0 +1,18 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"
+  - package-ecosystem: "gomod"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      gomod:
+        patterns:
+          - "*"