docs: bifurcate documentation into user, admin, and developer sections

Major restructuring of documentation to separate concerns:

**New Structure:**
- `/docs/` - User-facing docs (intro, quickstart, databases, using-superset, faq)
- `/admin-docs/` - Administrator docs (installation, configuration, security)
- `/developer-docs/` - Developer docs (contributing, extensions, guidelines, testing)

**Changes:**
- Move installation, configuration, and security docs to admin_docs/
- Move contributing, extensions, guidelines, and testing to developer_docs/
- Rename developer_portal to developer_docs (with underscore to hyphen in URL)
- Add sidebarAdminDocs.js for admin documentation navigation
- Update versions-config.json with new doc sections
- Update docusaurus.config.ts with new plugins and redirects
- Update internal links in versioned docs (6.0.0) to use new paths
- Keep user-facing content (databases, using-superset, faq) in main docs

This separation makes it clearer which documentation is relevant for:
- End users exploring and visualizing data
- Administrators deploying and configuring Superset
- Developers contributing to or extending Superset

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/versioned_docs/version-6.0.0/configuration/sql-templating.mdx

@@ -10,7 +10,7 @@ version: 1
 ## Jinja Templates
 
 SQL Lab and Explore supports [Jinja templating](https://jinja.palletsprojects.com/en/2.11.x/) in queries.
-To enable templating, the `ENABLE_TEMPLATE_PROCESSING` [feature flag](/docs/configuration/configuring-superset#feature-flags) needs to be enabled in
+To enable templating, the `ENABLE_TEMPLATE_PROCESSING` [feature flag](/docs/6.0.0/configuration/configuring-superset#feature-flags) needs to be enabled in
 `superset_config.py`. When templating is enabled, python code can be embedded in virtual datasets and
 in Custom SQL in the filter and metric controls in Explore. By default, the following variables are
 made available in the Jinja context: