Improves the formatting of the Terraform plugin's `tf_prompt_info()`
function (see #6373 and #6418). It:
- adds a `tf:` prefix to indicate that what follows is the Terraform
workspace
- adds colorization and formatting to make the appearance more similar
to the `git-prompt` plugin
- adds a trailing space to separate the prompt from user input
* Fix the terraform function name
Current function name do worse. I always use `terr<TAB>` and before those prompt it was add space in the end. Now because we have multiple functions and binaries started with terraform there are no space.
* Updated terraform readme
Updated the name of new function name
