helper funcs for converting rootcfgs to terraform roots

[smonero]

• Note that I don't think we need things like TriggerInfo and plan mode so we don't set them.
• Also I just use the string representations from the deploy package rather that copy/pasting them (EnvStep, Manifest, etc)
• We could also use a WorkflowSignaler with TemporalClient nil to use the helper funcs like prependPlanEnvSteps but I figured it would be more straightforward to just copy them
• We can also potentially move things to an internal folder similar to what is done with the pr and deploy flows, this would require changing some of the imports but not sure if that is even useful
• Originally I wanted to reuse the structs from the deploy and pr flows (i.e. root, repo, step, etc), I decided to go with the deploy version rather than the pr version because deploy has the Apply job. However I am not 100% sure if that is actually necessary.

relies on #732 and #743 to be merged first, then we will be able to actually use these funcs.

[samrabelachew]

Can you write tests for these changes?