Add header-checking function (#9880)

* Add basic header-checking function

* Add Slack notification logic

* Modify Netlify Functions setup

* Rework function logic

* Add missing dependencies

* Remove package-lock.json from Git

* Separate header checking function

* Isolate env check into a separate function

netlify.toml

@@ -3,6 +3,7 @@
 # It is turned off for only for the production site by using [context.master] below
 # DO NOT REMOVE THIS (contact @chenopis or @sig-docs-maintainers)
 publish = "public"
+functions = "functions"
 command = "make non-production-build"
 
 [build.environment]