[API]: Add primary headings to Docs search responses

[AugustMiller]

Product

Other/Multiple/Not Sure

Description

Documentation API search queries should include the top-level headings (often called the "table of contents" in Markdown parsers) with anchors and/or fully-formed direct URLs (as seen under the proposed headings key):

{
    "id": 826167,
    "title": "Application Configuration",
    "url": "https://craftcms.com/docs/5.x/reference/config/app",
    "uri": "docs/5.x/reference/config/app",
    "slug": "app",
    "type": "Craft CMS 5.x / Reference / Configuration Reference",
    "summaryPlain": "Craft’s entire application configuration can be customized via config/app.php. Any items returned by an app.php config file will get merged into the main application configuration array.",
    "summaryHtml": "Craft’s entire <a href=\"guide:structure-applications#application-configurations\">application configuration</a> can be customized via <code>config/app.php</code>. Any items returned by an <code>app.php</code> config file will get merged into the main application configuration array.",
    "headings": [
        { "level": 2, "name": "approach", "text": "Approach", "url": "https://craftcms.com/docs/5.x/reference/config/app#approach" },
        { "level": 2, "name": "requests-responses", "text": "Requests + Responses", "url": "https://craftcms.com/docs/5.x/reference/config/app#requests-responses" },
        { "level": 3, "name": "cors", "text": "CORS", "url": "https://craftcms.com/docs/5.x/reference/config/app#cors" }
    ]
}

We are currently testing the Heading Permalinks extension, and should be able to capture or generate all of this, as the text is rendered.

[linear]

PT-3067