feat: Add Docusaurus renderer

[julian-risch]

This PR adds a DocusaurusRenderer. It's simpler than ReadmeCoreRenderer because it doesn't intera.ct with any Readme API

I got the feedback from @dfokina that the following frontmatter is enough for docusaurus as a start. The id should come from what was the slug field before. For example, in agents_api.yml we have slug: agents-api. I renamed it to id.

---
title: "Creating Custom Components"
id: "custom-components"
description: "Create your own components and use them standalone or in pipelines."
---

Tested with

loaders:
  - type: haystack_pydoc_tools.loaders.CustomPythonLoader
    search_path: [../../../haystack/components/agents]
    modules: ["agent"]
    ignore_when_discovered: ["__init__"]
processors:
  - type: filter
    expression:
    documented_only: true
    do_not_filter_modules: false
    skip_empty_modules: true
  - type: smart
  - type: crossref
renderer:
  type: haystack_pydoc_tools.renderers.DocusaurusRenderer
  description: Tool-using agents with provider-agnostic chat model support.
  title: Agents
  id: agents-api
  markdown:
    descriptive_class_title: false
    classdef_code_block: false
    descriptive_module_title: true
    add_method_class_prefix: true
    add_member_class_prefix: false
    filename: agents_api.md

which generated

---
title: Agents
id: agents-api
description: Tool-using agents with provider-agnostic chat model support.
---

<a id="agent"></a>

# Module agent

<a id="agent.Agent"></a>

## Agent

A Haystack component that implements a tool-using agent with provider-agnostic chat model support.
...