[WIP] add a Terraform module interface

[displague]

This experimental branch adds a terraform module interface to packet-cli.
The goal of this is to make it easier to consume Packet provider modules from the official Terraform registry.

Only github.com/packethost and github.com/packet-labs modules would be considered.

_Update: Only the Equinix Metal provider and Equinix modules would be considered)

Current blockers

• Hashicorp/terraform does not expose a "modules list" function.

Considerations

• This adds a ton of dependency. Can packet terraform be built as an independent plugin through a plugin interface (like git plugins)? (possibly a shell script?)

Future workflow

Examples of use:

list all Packet modules

$ packet terraform get

show module details

The registry API includes the parameters of the module.

$ packet terraform get kubernetes-bgp
+----------------+---------+
|     SOURCE     | VERSION |
+----------------+---------+
| kubernetes-bgp | 0.0.1   |
+----------------+---------+

create an instance of that module

These module parameters could be exposed as arguments.

This would effectively perform terraform init --from-module=packet/k8s/packet.
What directory would this go in? Should the base directory be common - and pass workspace through? (Likening this to go get, this would be like go get registry/module@workspace)

The api token would be wired-up, since the packet cli already knows one. How does it do this? Well known APIKey / Token variable names?

$ packet terraform create k8s --workspace foo --facility ewr1

[displague]

Hashicorp/terraform does not expose a "modules list" function.

Depite the limitations from https://github.com/hashicorp/terraform/tree/main/internal/initwd not being public, there are several workarounds:

• don't list modules, take whatever parameters are supplied and assume that equinix/$1/metal is a valid module. take all -- arguments that are not recognized and produce a terraform.tfvars with these values
• bundle the terraform plugin with known module help scripts, each can validate the parameters to the variables supported by the module. Each script can also translate packet-cli variables (token) to the name of the variable in each specific module (metal_auth_token, auth_token, etc).

[displague]

@ctreatma found https://github.com/hashicorp/terraform-config-inspect which may be a suitable workaround for the https://github.com/hashicorp/terraform/tree/main/internal/initwd concerns mentioned above.