Fix `az ad app permission grant` in the docs

[dgroh]

Describe the bug
The docs for az ad app permission add says to invoke az ad app permission grant, but when invoking it a 404 error is shown. Workaround is to use az ad app permission admin-consent instead.

To Reproduce

Run the follwoing commands with powershell:

 $appRegistration = az ad app create `
     --display-name "AppName" `
     --reply-urls "http://localhost/auth" `
     --oauth2-allow-implicit-flow true `
     --available-to-other-tenants false `
     -o json | 
 ConvertFrom-Json

 az ad app permission add --id $appRegistration.appId `
     --api '00000003-0000-0000-c000-000000000000' `
     --api-permissions @("c5366453-9fb0-48a5-a156-24f0c49a4b84=Scope", "1ca167d5-1655-44a1-8adf-1414072e1ef9=Scope")

 az ad app permission grant --api 00000003-0000-0000-c000-000000000000 --id $appRegistration.appId

This error is showing:

There is a related issue on StackOverflow about it from a months ago: https://stackoverflow.com/questions/62883453/add-graph-api-via-az-ad-app-permission-fails

Expected behavior
The doc should specify when to exactly use it. In case the issue is with the cli, this should be fixed.

Environment summary
Powershell and Azure CLI 2.21.0

Additional context

[yonzhan]

Jiashuo Li (@jiasli) for awareness

[jiasli]

The error was refined in #17051. Please see #16862 (comment) for the solution.