[Data Usage] New plugin (#193466)

The initial serverless only plugin for viewing data usage and retention
in Management. The purpose of this PR is to provide a place for other
engineers to work on it, hidden from public use.

- Plugin is hidden by default and can be enabled through kibana.yml
`xpack.dataUsage.enabled: true`
- Currently it will show up in both stateful and serverless (if enabled
using config above). When we are ready to make the plugin available we
will enable it in config/serverless.yml
- Renders a card in Management (serverless) when enabled:
<img width="1269" alt="Screenshot 2024-09-19 at 4 14 15 PM"
src="https://github.com/user-attachments/assets/705e3866-bc88-436a-8532-2af53167f7b1">


https://github.com/elastic/kibana/issues/192965
https://github.com/elastic/kibana/issues/192966

---------

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

docs/developer/plugin-list.asciidoc

@@ -536,6 +536,10 @@ Plugin server-side only. Plugin has three main functions:
 |In order to make ongoing maintenance of log collection easy we want to introduce the concept of data set quality, where users can easily get an overview on the data sets they have with information such as integration, size, last activity, among others.
 
 
+|{kib-repo}blob/{branch}/x-pack/plugins/data_usage/README.md[dataUsage]
+|Serverless only plugin for users to view data usage
+
+
 |{kib-repo}blob/{branch}/x-pack/plugins/data_visualizer/README.md[dataVisualizer]
 |The data_visualizer plugin enables you to explore the fields in your data.