chore: add blueprint to add a .github repo

blueprints/add-dot-github-repo.yml

@@ -0,0 +1,22 @@
+id: add-dot-github-repo
+name: Ensures that a .github repo is present in the GitHub organization.
+description: |-
+  This will add a `.github` repository for the project. Such a repository is useful to define some defaults for all repositories
+  within a GitHub organization or share common reusable workflows. There is no restriction wrt settings to this repository, this blueprint
+  will only check for the existence of such a repository and it can be modified as usual.
+type: append_configuration
+config:
+  condition: >-
+    $count(
+      $.repositories[name = ".github"]
+    ) = 0
+  content: |-
+    {
+      # snippet added due to '{{blueprint_url}}'
+      _repositories+:: [
+        orgs.newRepo('.github')
+      ],
+    }
+  reviewers:
+    - "{{project_name}}-project-leads"
+    - "{{project_name}}-committers"