CEXT-5668: Introduces the App Management documentation section

[danidelcar]

Purpose of this pull request

This PR introduces the App Management documentation section, providing comprehensive guidance for developers and merchants on installing, configuring, and managing App Builder applications in Adobe Commerce.

Summary of changes

New documentation section: App Management

Created four new documentation pages under /src/pages/app-management/:

File	Description
index.md	Overview of App Management with key benefits, requirements, and how it works
app-metadata.md	Reference for defining metadata in app.commerce.config
configuration-schema.md	Reference for defining configuration schemas in app.commerce.config
runtime-actions.md	Guide to initializing the configuration library and understanding auto-generated runtime actions
associate-apps.md	Instructions for associating apps with Commerce instances and configuring business settings

All pages include a beta warning banner:

Adobe Commerce App Management is for Beta users only and is not yet accessible to all customers.

And a new metadata keyword: App Management

Additional info

JIRA CEXT-5668
Preview branch

[keharper]

I don't understand the audience. Is it for developers for packaging their apps? Merchants who have purchased an app?

[iivvaannxx]

I think it's good we encourage usage of the init script, that's what I wrote it, to automate the burden of all the manual steps required. But I feel we should document the actual manual setup so developers understand it end-to-end.

The script does a lot of "magic" and that can cause confusion if something fails. If developers understand what the script is doing, they can ensure everything is correctly configured by themselves.

This is what it's done in the usage guide.