Allow multiple compute environment resources in an app model

[eerhardt]

Description

Add IComputeResource and IComputeEnvironmentResource interfaces.

This pull request introduces support for compute environment resources and how to model multiple compute environments in a single app. If there are multiple compute environments, users need to explicitly mark each compute resource .WithComputeEnvironment(env) to specify which environment is for which compute resource. An exception will be raised if there are multiple environments without specifying which one.

Contributes to #8786

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
• Does the change make any security assumptions or guarantees?
  • No
• Does the change require an update in our Aspire docs?
  • No