chore(docs): add llms.txt (#10133)

This pull request enhances the documentation site configuration by
introducing a new plugin and making minor adjustments to existing
settings. The primary focus is on integrating the
`@signalwire/docusaurus-plugin-llms-txt` plugin to improve content
handling and adding relevant dependencies.

### Plugin Integration:

*
[`docs/docusaurus.config.js`](diffhunk://#diff-28742c737e523f302e6de471b7fc27284dc8cf720be639e6afe4c17a550cd654R245-R255):
Added the `@signalwire/docusaurus-plugin-llms-txt` plugin with
configuration options, including a depth of 3, log level of 1, exclusion
of certain routes, and enabling markdown file support.
*
[`docs/package.json`](diffhunk://#diff-adfa337ce44dc2902621da20152a048dac41878cf3716dfc4cc56d03aa212a56R33):
Included the `@signalwire/docusaurus-plugin-llms-txt` dependency
(version `^1.2.0`) to support the new plugin integration.

### Configuration Adjustments:

*
[`docs/docusaurus.config.js`](diffhunk://#diff-28742c737e523f302e6de471b7fc27284dc8cf720be639e6afe4c17a550cd654L221):
Removed the `docItemComponent` property under the `module.exports`
configuration.

docs/docusaurus.config.js

@@ -218,7 +218,6 @@ module.exports = {
           showLastUpdateTime: true,
           editUrl: "https://github.com/zitadel/zitadel/edit/main/docs/",
           remarkPlugins: [require("mdx-mermaid")],
-
           docItemComponent: "@theme/ApiItem",
         },
         theme: {
@@ -243,6 +242,17 @@ module.exports = {
         },
       },
     ],
+    [
+      "@signalwire/docusaurus-plugin-llms-txt",
+      {
+        depth: 3,
+        logLevel: 1,
+        content: {
+          excludeRoutes: ["/search"],
+          enableMarkdownFiles: true,
+        },
+      },
+    ],
     [
       "docusaurus-plugin-openapi-docs",
       {