Added blanket codeowners for broad directories (oppia#9977)

* Modified codeowners file

* addressed comments

.github/CODEOWNERS

@@ -13,9 +13,27 @@
 #   lead listed on the page above).
 
 
+# Blanket codeowners
+# This is for the case when new files are created in any directories that aren't
+# covered as a whole, since in these cases, codeowners are not recognized for
+# those files when reviewing, even if the PR does add it. Unless new
+# files/folders are created in the following directories, these codeowners would
+# be superseded by the relevant codeowners mentioned elsewhere in this file.
+# (Reference: https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners)
+/core/controllers/ @aks681
+/core/domain/ @DubeySandeep
+/core/templates/components/ @bansalnitish
+/core/templates/domain/ @kevintab95
+/core/templates/pages/ @seanlip
+/core/templates/services/ @nithusha21
+/extensions/ @vojtechjelinek
+/scripts/ @ankita240796
+
+
 # Android team
 /core/domain/android_validation_constants*.py @BenHenning
 
+
 # Angular Migration team
 /core/templates/components/shared-component.module.ts @bansalnitish @srijanreddy98
 /core/templates/services/loader.service*.ts @bansalnitish @srijanreddy98