Move scripts used in CI to the new location (#5198)

* Move CI scripts and update references

* Update paths in .gitlab-ci.yml

* Removed outdated entries from CODEOWNERS

polkadot/scripts/ci/github/lib.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+# Gets the runtime version for a given runtime from the filesystem.
+# Optionally accepts a path that is the root of the project which defaults to
+# the current working directory
+def get_runtime(runtime: nil, path: '.', runtime_dir: 'runtime')
+  File.open(path + "/#{runtime_dir}/#{runtime}/src/lib.rs") do |f|
+    f.find { |l| l =~ /spec_version/ }.match(/[0-9]+/)[0]
+  end
+end