Spin off configuration schema generator as a standalone package

Autocomplete of Aspire configs in appsettings.json is fantastic as my project is growing. I would love to have this capability in my projects as well. Also, I'm using keyed component resolution and the default Aspire schema doesn't know what's the key I'm using in my code. Looks like this capability is handled by the configuration schema generator introduced in #1383 . The team should consider spinning off this capability as an extension package for 3P usage.

Start by reading issue #1383 and locating the existing configuration schema generator used for appsettings.json autocomplete. Define the standalone extension package boundary, including support for keyed component resolution; done means third-party projects can use the capability with their own keys.

Written by the indexing model from the issue text.