Init command to help old docs transition

[pedro-psb]

Feature

As a pulp plugin maintainer, I want to have an easy-to-follow and predictable way of migrating old to new docs, regardless if I already use markdown or not.

Requirements

• [ ] Implement pulp-docs transition init (or similar name):
  • [ ] Make dir tmp_docs/
    • contain markdown version of the old docs content.
    • If old docs was in .rst, it should be converted first.
  • [ ] Make dir staging_docs/
    • contain the structure defined in the design docs
  • [ ] If one of these folders already exists, abort and instruct the user to clean them if they like to re-initialize (or do some similar safe guard to avoid accidental overwrite)

Context

• Here is a quick overview of the motivation of having a tmp_docs folder: https://miro.com/app/board/uXjVN8JT3bU=/?moveToWidget=3458764574957791463&cot=14

[pedro-psb]

These helpers will be available elsewhere (in migration guides). Its a lightweight process, anyway