Add validations for UAMI requirement

[saanikaguptamicrosoft]

Notes

• Foundry training jobs require a UAMI on the project for submit operation. This PR surfaces it early as a warning during init/override, and blocks submit upfront when we know the project lacks one.
• Env caching strategy:
  • Caches result in AZURE_AI_TRAINING_HAS_UAMI to avoid an ARM call on every submit.
  • Lazy-resolves when missing
  • Tolerates ARM failures (proceeds without blocking).

Testing

• If UAMI is missing during init flow

• If UAMI is missing during azd env override flow

• If AZURE_AI_TRAINING_HAS_UAMI is not already set, Submit call makes a call to ARM API and set it

• After setting AZURE_AI_TRAINING_HAS_UAMI as false, the Submit call fails upfront with right messaging