fix: allow init cmd to pull vars from cloud

[ctrombley]

DO NOT MERGE

Terraform 1.15.0-beta2 is able to resolve dynamic module sources in config using variables.

When a new config is created with a cloud block, terraform init needs to be run to generate the lock file that will resolve the dynamic module sources. If a dynamic module source has been used, the resolved module source is based on the variable values passed. Currently, the only way to pass values locally is via -vars or -var-file (both now supported by the init command).

But since the cloud block already references a workspace, terraform should also be able to resolve hcpt or tfe variables from that workspace to use as context when resolving the module sources.

AC: We should pull the workspace vars from hcpt/tfe during init when a variable has been defined in config but doesn't have values passed via -vars or var-file.

[github-actions]

Changelog Warning

Currently this PR would target a v1.16 release. Please add a changelog entry for in the .changes/v1.16 folder, or discuss which release you'd like to target with your reviewer. If you believe this change does not need a changelog entry, please add the 'no-changelog-needed' label.