preview: first take to handle bump preview command 🎉

[paulRbr]

This is the implementation of the preview command with a lot of simplification from the original ruby CLI.

It removes:

• the --specification flag because the server now knows how to guess from the given file
• the --validation flag because the server will now only do the 'basic' validation (cf https://github.com/bump-sh/bump/issues/522)
• the --no-external-refs flag because the new node CLI handles all external refs

The resulting command can be summarised by its help:

Create a documentation preview for the given file

USAGE
  $ bump preview FILE

ARGUMENTS
  FILE  Path or URL to your API documentation file. OpenAPI (2.0 to 3.0.2) and AsyncAPI (2.0)
        specifications are currently supported.

OPTIONS
  -h, --help  show CLI help

EXAMPLE
  $ bump preview FILE
  * Your preview is visible at: https://bump.sh/preview/45807371-9a32-48a7-b6e4-1cb7088b5b9b

🎉

Closes #1

[Polo2]

I just left a small comment about OpenAPI version,
while I was reading this whole PR for my education.

[scharrier]

I did a second review, sorry for the ping/pong. I left some important (I think) comments. It's far easier to understand comparing to the first version.

I think that we still can enhance some stuff to make it even clearer.

Another small note: I think that we should try to do atomic PRs when we can. This means extracting any not directly related changes to other smaller PRs. Small/atomic PRs make reviewing a bit easier and merging faster. This is the first one so I totally get why it's a big one, but for the upcoming ones, I'm sure that we can do smaller ones.

Congrats on this huge work, I'm pretty sure that we'll be able to merge something tomorrow! 👏

[scharrier]

I left some small comments and questions, but nothing that should block this PR (it's more for my personal knowledge and to be sure that it's not stuff you forgot).

You got the LGTM, let's merge this! 👏

[paulRbr]

You got the LGTM, let's merge this! clap

Thanks for the review (and the patience) 😃