Hooks for certain resources to handle cases like the "association" resources

[magodo]

There are some special terraform resources in the AzureRM provider, which is not a concrete Azure resource, but some logical concept to "associate" two concrete resources. Propose to add some kind of hooks to support them.

[magodo]

With #231 merged, there is now an proper place to put such logic to: https://github.com/Azure/aztfy/blob/4d45e8416c06ecc6b643748bef1d6280b11672e4/internal/resourceset/azure_resource_set_hack.go#L22

Currently, the azurerm_virtual_machine_data_disk_attachment is supported, we will need to support the others. The full list can be found at: https://github.com/magodo/aztft/blob/3dfe6a12ed5ee515b6f9281ed307c54211ee35b3/tool/aztft-import/main.go#L45.

Note:

1. If populating the "master" resource needs its API body, we should also add it to the PopulateResourceTypesNeedsBody
2. The association resource will eed an Azure resource id](https://github.com/Azure/aztfy/blob/4d45e8416c06ecc6b643748bef1d6280b11672e4/internal/resourceset/azure_resource_set_hack.go#L94). This azure resource id is a hypothetic one, while we have to make sure it is of unique format. As Azure resource id will be used as the key in a lot of places.

[magodo]

Per #238, the logic about discovering property-like resources are now offloaded to aztft. This helps to keep the code base clean and centralize all those azurerm provider resource specific details to aztft.