github: Create CODEOWNERS file (#457)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
new file mode 100644
index 0000000..37502e3
--- /dev/null
+++ b/.github/CODEOWNERS
@@ -0,0 +1,3 @@
+# This codebase has shared ownership and responsibility.
+
+* @hashicorp/terraform-core @hashicorp/terraform-devex @hashicorp/tf-editor-experience-engineers