aspire destroy: Add --no-wait flag for async Azure resource group deletion

## Summary

`aspire destroy` now waits for Azure resource group deletion to complete by default (`WaitUntil.Completed`). This can take several minutes for large resource groups.

For CI/automation scenarios where the caller doesn't need to wait, a `--no-wait` flag would allow fire-and-forget deletion (the previous `WaitUntil.Started` behavior).

## Proposed behavior

- **Default (no flag):** Wait for RG deletion to complete before reporting success
- **`--no-wait`:** Initiate deletion and return immediately with a message like "Resource group deletion started"

## Context

Follow-up from #16097. The default was changed from async to sync deletion to avoid confusing "deletion initiated" messaging and stale-state issues on immediate redeploy.