front-door apis fundamentally broken

- If the issue is to do with Azure CLI 2.0 in-particular, create an issue here at [Azure/azure-cli](https://github.com/Azure/azure-cli/issues)

### Extension name
front-door

### Description of issue (in as much detail as possible)
The front-door API design seems fundamentally broken in that the patterns are very inconsistent - some things have to created and passed to the methods in order to create them. Other things create their children for you but without letting you pass settings to that child object.

All this means you end up with something in a state you do not want which you either have to rectify manually through the portal, or by scripting creation of extra resources and then going back and deleting the ones you do not want.

Here are just some examples I have come across:
- `front-door`
- `create` requires a `backend-address` and sets up a host, backend-pool and routing-rule for you but I cannot provide any additonal settings to control how these are configured
- it also creates a `frontend-endpoint` for you but I am unable to pass the `waf-policy` to this, and the `frontend-endpoint` has no `update` command meaning I can't set this retrospectively
- This means I now have to **update this manually in the portal**
- `backend-pool`
- To create a backend-pool I first have to create `load-balancing` and `probe settings` (this is done for you and this concept isn't explicitly exposed in the portal)
- however I have to provide the `--address` option which creates a `backend` for me

I would ideally like it so that it only creates what I ask for. But if it must create child resources then all options should be available - or there should be someway to edit these child resources.