[FTR] Refactor FTR to live under KBN-TEST (#42547) (#42788)

Refactor the FTR to live under KBN-TEST . 

Next, refactor any and all files that the
FTR needs to live under KBN-TEST,
as needed.

scripts/functional_test_runner.js

@@ -18,4 +18,4 @@
  */
 
 require('../src/setup_node_env');
-require('../src/functional_test_runner/cli');
+require('@kbn/test').runFtrCli();