`kctrl`: Post-alpha refactoring tracker for package authoring commands

[100mik]

Tasks at hand:

• [x] Refactor vendor utils to be a scoped struct with associated functions
• [x] Refactor workflows to move away from the step interface and update them according to refactoring described above
  • [x] Local directory
  • [x] Generic vendir step
  • [x] Git release workflow
  • [x] Files from git repo
  • [x] Helm chart from git repo
  • [x] Helm chart from OCI repository
• [x] Dedup and break up package init logic into smaller pieces
• [x] Move away from file utils and use existing art in in-built go packages (ioutil, os) instead
• [ ] Refactor existing structs into packages
• [ ] Handle how fetch option is passed between stages better
• [ ] Verify that there is no regressions through means of existing tests and a bit of manual testing

[100mik]

This is branching out from work that was ongoing in #766 In favour of breaking it down into digestible pieces and pulling in the authoring commands into an alpha release for early adopters.