[UX] Improve validation warning to reduce deployment failures

**Problem**

During azd up, we surface validation warnings before deployment. Many users dismiss these warnings and continue, but some warnings appear to correlate with deployment failures. While we can't say with certainty that every warning will lead to a failure, telemetry suggests that some warnings are much more likely to result in unsuccessful deployments.

Today, all warnings are presented similarly, making it easy for users to ignore them without understanding the potential impact.

**Goal**

Improve the validation warning experience so users are more likely to resolve important warnings before proceeding, reducing avoidable deployment failures.