[INFRA] Configure dependabot (#67)

Update GitHub Actions.

Author: tbouffard

.github/dependabot.yml

@@ -0,0 +1,19 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    # Workflow files stored in the default location of `.github/workflows`
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: wednesday
+    open-pull-requests-limit: 2
+    rebase-strategy: "disabled"    
+    commit-message:
+      prefix: "[INFRA] gha -"
+    reviewers:
+      - process-analytics/pa-collaborators