Complete az apim commands

**Is your feature request related to a problem? Please describe.**
Azure API Management is a critical, core service for creating modern web architectures, particularly when coupled with app service, functions, etc. The `az apim` module is missing nearly all required functionality to create and manage apis, policies, products, etc within apim. The feature request is to complete the module, to get it on parity with Powershell: https://docs.microsoft.com/en-us/powershell/module/azurerm.apimanagement/?view=azurermps-6.13.0

It is really unfortunate to use az cli for 95% of code and then switch to ARM/Powershell.

**Describe the solution you'd like**
Complete the `az apim` module to reach parity with ARM/Powershell (https://docs.microsoft.com/en-us/powershell/module/azurerm.apimanagement/?view=azurermps-6.13.0)

**Describe alternatives you've considered**
ARM or Powershell, but switching languages/platforms is cumbersome when the rest is using az cli.

**Additional context**
If possible, if this is planned or being planned, could you provide a timeline so that we can plan our roadmaps accordingly?