feat: add flag to optionally list pre-release versions

[mmourick]

What

• Adds --pre-release option to list subcommand to display pre-release versions of Terraform
• Changes list behavior by hiding pre-release versions by default.

Why

• Declutters the list of Terraform versions listed, as pre-releases are not relevant for the majority of users.

References

• Closes Hide pre-release versions from list unless indicated #19

[ChrisTerBeke]

There's a conflict with the main branch, did you rebase? All the color-coded output has been moved to helper functions :)

[mmourick]

@ChrisTerBeke Yeah had to resolve a small merge conflict, I've updated the PR now to use the new helper functions 👍

[ChrisTerBeke]

Nice!

In addition to the two comments in the code, it would be great if the help text (listExample) could be updated to include this new flag, as well as the README.