Add support for detecting OpenTofu version from .opentofu-version files. #677

Job	Run time
asdf	23s
latest	26s
TERRAFORM_VERSION range	21s
Local State file	21s
provider versions	36s
Remote State file	2m 30s
specific required_version	23s
required_version range	20s
required_version with a v prefix	20s
OPENTOFU_VERSION with terraform action	30s
TFC Cloud Configuration	49s
Partial TFC Cloud Configuration with tags	42s
Partial TFC Cloud Configuration	45s
TFC Workspace	35s
tfenv	24s
tfswitch	23s
tofuenv	25s
Prefer OpenTofu, but only Terraform matches constraints	27s
OPENTOFU_VERSION with tofu action	26s
OPENTOFU_VERSION pre-release with tofu action	27s
	11m 33s

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