docs: add Ansible IaC guide for tenant configuration (#759)

Document the community.ansible_netbird collection for managing NetBird
resources (users, groups, setup keys, policies, networks, DNS, posture
checks) declaratively via the REST API. Adds a new Infrastructure as
Code subsection under Self-Host NetBird with room for future entries.

Cross-links from the Automated Setup PAT bootstrap page since the
collection is the natural next step after obtaining the first token.

src/components/NavigationDocs.jsx

@@ -540,6 +540,13 @@ export const docsNavigation = [
         links: [
             { title: 'Quickstart Guide', href: '/selfhosted/selfhosted-quickstart' },
             { title: 'Automated Setup', href: '/selfhosted/automated-setup' },
+            {
+                title: 'Infrastructure as Code',
+                isOpen: false,
+                links: [
+                    { title: 'Ansible', href: '/selfhosted/iac/ansible' },
+                ],
+            },
             {
                 title: 'Cloud Marketplaces',
                 isOpen: false,