Add support for TERRAFORM_BINARY_NAME environment variable for use with OpenTofu

[RFHold]

CDKTF has an environment variable TERRAFORM_BINARY_NAME documented here. It can be used to supply "tofu" to use the OpenTofu fork of Terraform.

The two are largely compatible with each other and I believe it should be as simple as replacing the executable you have defined in your state code.

[idoavrah]

Hi Robert,

Thank you for opening this issue. Just to clarify what you're saying, are you suggesting I add the new environment variable as an alternative to issuing the executable via the -e flag, or am I missing something else? I'm not a CDKTF or opentufo user myself, and I don't see the direct connection to TFTUI.