Update docs to centralize on ARM-based Azure provider (#7767)
Update docs to centralize on ARM-based Azure provider (#7767)

Sidebar:

 - Rename "Azure (Resource Manager)" to "Microsoft Azure" and sort
   accordingly
 - Rename "Azure (Service Management)" to "Microsoft Azure (Legacy ASM)"
   and sort accordingly

ARM provider docs:

 - Name changes everywhere to Microsoft Azure Provider
 - Mention and link to "legacy Azure Service Management Provider" in opening paragraph
 - Sidebar gains link at bottom to Azure Service Management Provider

ASM provider docs:
 - Name changes everywhere to Azure Service Management Provider
 - Sidebar gains link at bottom to Microsoft Azure Provider
 - Every page gets a header with the following
 - "NOTE: The Azure Service Management provider is no longer being actively developed by HashiCorp employees. It continues to be supported by the community. We recommend using the Azure Resource Manager based [Microsoft Azure Provider] instead if possible."
sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,sebastus/terraform-provider-azurerm