[feat][doc] Separate CLI docs for doc gen automation

[Anonymitaet]

This is part work of PIP 78: Generate Docs from Code Automatically

Docs in the green circle are updated manually and shown independently on https://pulsar.apache.org/reference/#/latest/, so do not care about the metadata in .md files.

Metadata example:

---
id: reference-cli-pulsar-shell
title: Pulsar CLI tools - pulsar-shell
sidebar_label: "cli-pulsar-shell"
---

Documentation

• doc

[Anonymitaet]

@SignorMercurio

1. Could you please review this PR from a technical perspective? Thank you!

2. Once this PR gets merged, we need to show the content (in the green box) on https://pulsar.apache.org/reference/#/latest/ ASAP? Or else users can not see them

cc @D-2-Ed @DaveDuggins

[Anonymitaet]

FYI: @SignorMercurio @urfreespace

I've confirmed with @codelipenghui, broker-tool is moved to pulsar-admin broker-stats

So I'll remove reference-cli-broker-tool.md, which means this section will not be available on the Reference site.

[tisonkun]

1. We'd better use /reference than https://pulsar.apache.org/reference here.
2. We should find a way to generate version part (latest) so that when the next version become a stable version, it doesn't direct users to the latest reference pages.

[tisonkun]

Perhaps we can use @pulsar:version@ magic var but I think it cannot be resolved as latest. Maybe @pulsar:docversion? But there will be an issue between latest and next. We should unify names here.

[SignorMercurio]

We can change latest to next, but may not be able to use /reference as it may be parsed by Docusaurus as a markdown docs rather than an external link to another site.

[tisonkun]

@SignorMercurio Let's do the first part.

I'm thinking of that you can directly move the docsify folder under website-next/static/ and we can preview the references pages also. You can give it a try. And perhaps several build logics should be modified.