azd x init treats extension metadata warnings as build failures

[JeffreyCA]

Summary

azd x init fails when an extension selects the Service Target Provider capability because azd x build treats metadata validation warnings as command-failing errors.

Repro

1. Run azd x init.
2. Select the Service Target Provider capability.
3. Let init continue into the build step.

Actual

The build step fails/skips the remaining flow due to a validation warning such as:

Error: Validation warnings
Details:
Extension contains validation warnings: Missing providers

When invoked through azd x init, the useful warning details may not be surfaced clearly and the command flow stops.

Expected

Validation warnings should be displayed as warnings only. They should not fail azd x build or stop the azd x init flow; build/package/install should proceed unless there are validation errors.