Make it easier to find locations where ACA is available

**Related command**
`az provider show locations`

**Is your feature request related to a problem? Please describe.**
ACA is not available in all locations, and it saves a lot of time if a user can see where it is available before attempting a deployment.
The current command is pretty unintuitive and hard to remember:
`az provider show -n Microsoft.App --query "resourceTypes[?resourceType=='managedEnvironments'].locations"`

**Describe the solution you'd like**
We should have something that is simple and easy to remember like this:
`az provider show locations -n ContainerApps`

There should also be a command/param to filter to regions that not only have ACA deployed, but also have available capacity:
`az provider show locations available -n ContainerApps`
or
`az provider show locations -n ContainerApps -onlyAvailable`
(There is probably already a pattern for this, just providing a couple of examples.)

**Describe alternatives you've considered**
I've asked around and the ugly command above is the best anyone could think of.