Beats Management plugin: migrate server-side code (elastic#70930)

* move all the legacy codebase to KP plugin

* fix imports

* add empty handler context & rename routes folder

* start migrating routes

* migrate rest of the routes

* migrate adapters

* remove beats from legacy xpack plugin

* use nullable + replace response.custom

* fix wrapRouteWithSecurity, remove incorrect header validation

* remove comment

* updating generated plugin list

* fix typos in doc

* adapt readme too.

* remove old commented routes from route files

* remove eslint disabling

* use camel case for plugin id

* update generated doc

Co-authored-by: Josh Dover <[email protected]>
# Conflicts:
#	x-pack/legacy/plugins/beats_management/server/rest_api/beats/configuration.ts
#	x-pack/legacy/plugins/beats_management/server/rest_api/configurations/upsert.ts

docs/developer/architecture/code-exploration.asciidoc

@@ -313,9 +313,10 @@ To access an elasticsearch instance that has live data you have two options:
 WARNING: Missing README.
 
 
-- {kib-repo}blob/{branch}/x-pack/plugins/beats_management[beats_management]
+- {kib-repo}blob/{branch}/x-pack/plugins/beats_management/readme.md[beatsManagement]
 
-WARNING: Missing README.
+Notes:
+Failure to have auth enabled in Kibana will make for a broken UI. UI-based errors not yet in place
 
 
 - {kib-repo}blob/{branch}/x-pack/plugins/canvas/README.md[canvas]

x-pack/index.js

@@ -7,9 +7,8 @@
 import { xpackMain } from './legacy/plugins/xpack_main';
 import { monitoring } from './legacy/plugins/monitoring';
 import { security } from './legacy/plugins/security';
-import { beats } from './legacy/plugins/beats_management';
 import { spaces } from './legacy/plugins/spaces';
 
 module.exports = function (kibana) {
-  return [xpackMain(kibana), monitoring(kibana), spaces(kibana), security(kibana), beats(kibana)];
+  return [xpackMain(kibana), monitoring(kibana), spaces(kibana), security(kibana)];
 };