[ML] Removing global isServerless flag (#166651)

Removed `isServerless` flag which lived in our global context and had to
be passed about to the various components which create their own version
of the context using `getMlGlobalServices`
This PR adds a new context which contains flags for all of the features
which can be toggled when in serverless mode.
Flags added:
```
 showNodeInfo
 showMLNavMenu
 showLicenseInfo
 isADEnabled
 isDFAEnabled
 isNLPEnabled
```
The enabled features flags are now read from the config file client
side, rather than using capabilities.

Additional changes:
- Changes the wording of the awaiting ML node callout in serverless.
- In the search project, the default ML page is the trained models list
and not Overview
- Reenables the Memory Usage page for all projects

---------

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

test/plugin_functional/test_suites/core_plugins/rendering.ts

@@ -258,6 +258,9 @@ export default function ({ getService }: PluginFunctionalProviderContext) {
         'xpack.license_management.ui.enabled (boolean)',
         'xpack.maps.preserveDrawingBuffer (boolean)',
         'xpack.maps.showMapsInspectorAdapter (boolean)',
+        'xpack.ml.ad.enabled (boolean)',
+        'xpack.ml.dfa.enabled (boolean)',
+        'xpack.ml.nlp.enabled (boolean)',
         'xpack.osquery.actionEnabled (boolean)',
         'xpack.remote_clusters.ui.enabled (boolean)',
         /**