Integrate with terraform-client-go for hcl only mode to eliminate terraform binary

[magodo]

Integrate with terraform-client-go for hcl only mode to eliminate terraform binary. This improves the performance (quicker speed and lower footprint) of importing.

To use it, users have to explicitly specify a new hidden flag (--tfclient-plugin-path). This flag is hidden since it is not supposed for CLI users to use, but is meant to be used by module users who wants to get the benefit of performance improvement.

Benchmark

Following tests are done on a Dell workstation that has 8 hyperthread cores and 24G RAM. The provider is a locally built, debug, un-stripped one. The commands being run are:

1. aztfexport rg -n -f -hcl-only --dev-provider aztfy-vmdisk

   (note the --dev-provider makes aztfexport to use a local provider, which also implies to skip any terraform init runs)

2. aztfexport rg -n -f -hcl-only -tfclient-plugin-path $HOME/go/bin/terraform-provider-azurerm aztfy-vmdisk

   (note the -tfclient-plugin-path implies aztfexport to use terraform-client-go instead of terraform binary, also it implies to using the same local provider)

The scale of the resource group being exported contains a typical VM setup, with a bunch of security rules, which ends up of 30 resources in total.

cgmemtime

Running cgmemtime for 10 times for each of above command:

1. Old

   Stat:

   • User Time : 45.991888888s
   • System Time : 5.189444444s
   • Wall Time : 34.252444444s
   • Child RSS high: 133.46MB
   • Group Mem high: 1.16GB

2. New

   Stat:

   • User Time : 1.004333333s
   • System Time : 86ms
   • Wall Time : 19.357777777s
   • Child RSS high: 126.45MB
   • Group Mem high: 159.74MB

[stemaMSFT]

LGTM for the most part, my only question is if customers are able to utilize this by default once the PR is merged or not. Would they have to expose the hidden flag? Assuming they have an easy way to utilize the optimizations in this PR I'll approve this.

[magodo]

@stemaMSFT Users can use the hidden flag if they will, though the flag won't show in the help message. The flag is necessary for specifying the path of the provider, otherwise, we don't know where the provider is...