Add network association resources

[simonbrady]

Ports the following resources from the current azurerm provider, making the minimum changes necessary to avoid any cascading dependency changes:

• azurestack_network_interface_security_group_association
• azurestack_subnet_network_security_group_association
• azurestack_subnet_route_table_association

This addresses #204 and updates the azurestack_subnet documentaton to address #195.

All acceptance tests pass on Azure Stack Hub 2206, and all documentation examples for the new resources deploy on this version.

Note that I've renamed the source files for azurestack_network_interface_security_group_association to match the resource name, and submitted this PR to make the corresponding change for the azurerm provider.

[FawenYo]

LGTM

[NeilBird]

Hi @simonbrady - Thanks for submitting this PR, it seems strange that ability to provision "azurestack_subnet" is missing from the v1.0.0 release. The associated you mentioned PR here, was successfully merged.

@tombuildsstuff - Are you able to review / approve this PR, as it would greatly improve v1.0.0, or perhaps it would justify a v1.1.0 release once tested? As without it there is no ability to provision using network_security_group_id and route_table_id for associations of SDN resources.

@katbyte - Would you have time be review / approve this PR? In addition to the above ask for @tombuildsstuff

[simonbrady]

Thanks for the comments @NeilBird - for tidiness's sake I've rebased this PR to ensure it still merges cleanly.

[matthew-hollick]

Hi all,

I'm new to using Terraform with Azurestack.
It looks like we are really stuck without this change.
Is it likely to make it into a release soonish?

Cheers,
Mat.