fix: pin @camunda8/docusaurus-openapi packages to 4.6.3 and revert Docusaurus 3.10.0 upgrade

@camunda8/docusaurus-theme-openapi-docs 4.6.4 pulls in @docusaurus/* 3.10.0
as transitive dependencies, which introduces a breaking React Context change
in Tabs (facebook/docusaurus#11733) causing SSG failures across all versioned
docs pages (ReactContextError at useDocsPreferredVersionContext).

Additionally, Docusaurus 3.10.0 renamed 'experimental_faster' to 'faster'
in the site config, which is incompatible with 3.9.x.

Pin the OpenAPI packages to exact 4.6.3 and keep Docusaurus at 3.9.2 until
the OpenAPI theme is updated for Docusaurus 3.10.0 compatibility.

Author: clementnero

docusaurus.config.js

@@ -11,7 +11,7 @@ module.exports = {
     v4: {
       removeLegacyPostBuildHeadAttribute: true,
     },
-    faster: true,
+    experimental_faster: true,
   },
   title: "Camunda 8 Docs",
   tagline: