Update documentation for az webapp deploy

**Related command**
az webapp deploy

**Is your feature request related to a problem? Please describe.**

In issue #29003 it seems that there are some dependency between the
**--async** and **--track-status** flags behaviour.

But this is not mentioned in the documentation for this command here https://learn.microsoft.com/en-us/cli/azure/webapp

My proposal is that this should be documented, because it is frustrating trying to debug this. I have spent hours trying to get the async deployment to work.

Perphaps also include more about what these flags do.

For the --async flag, please also include how (if possible?) I can poll for the status of the deployment.

**Describe the solution you'd like**
Would like to see these two flags to be documented better.

**Describe alternatives you've considered**

**Additional context**
azure-cli 2.62.0

core 2.62.0
telemetry 1.1.0

Extensions:
containerapp 0.3.53
interactive 0.5.3

Dependencies:
msal 1.28.1
azure-mgmt-resource 23.1.1