feat: run pipeform when running terraform plan

[suzuki-shunsuke]

This is still work in progress.

what

Run pipeform when running atmos terraform plan.

1. If the subcommand is plan, add the command line option -json and -out <plan file>
2. Run terraform plan and redirects the output to pipeform
3. Run pipeform
4. Run terraform show <plan file> to output the conventional output of terraform plan

why

Show the progress of terraform plan using pipeform.

references

• Implement pipeform for Terraform Operations #926

[suzuki-shunsuke]

This is still work in progress.

TODO:

• This feature depends on pipeform. For now users need to install pipeform by themselves. This is undesirable.
• Support atmos terraform apply as well
• Enable users to disable this feature

[suzuki-shunsuke]

Before reviewing the implementation details, we need to discuss the specification.
I've implemented the feature roughly for PoC and to clarify tasks.

[suzuki-shunsuke]

To pass the output of terrform plan to pipeform, I wanted to pass stdin and stdout to ExecuteShellCommand, but ExecuteShellCommand doesn't accept them.
So I defined a new function based on ExecuteShellCommand.
We should refactor later.

[suzuki-shunsuke]

I replaced pipeform command with Go package.

• feat: Support pipeform (Go package) #983