Allow multiple private-registries using az containerapp compose create

**Related command**
`az containerapp compose create --registry-server`

**Is your feature request related to a problem? Please describe.**
I'd love to use this command to quickly create an ephemeral version of our environment, but some of the images I want to pull in are from different registries. Rendering the command useless

**Describe the solution you'd like**
The ability to add multiple private registries to our compose. For instance `tenant_a.azurecr.io` & `our_own_tenant.azurecr.io`.

**Describe alternatives you've considered**
We're not sure how to use containerapp for our purpose. I've contemplated parsing the docker-compose.yml myself and creating the individual containers one-by-one but this seems kind of destined to fail.

**Additional context**
A more straightforward way to authenticate with container-registries would also be nice, now you're required to create tokens event though I'm already logged into the az-cli. Why can't I reuse those credentials?