feat: Authentik Terraform configuration for homelab SSO

Infrastructure as Code for Authentik identity provider managing:

OAuth2/OIDC Applications:
- Grafana, Home Assistant, Immich
- Uptime Kuma (proxy auth)
- Sonarr, Radarr, Prowlarr (*arr stack proxy auth)
- ArgoCD

Identity Sources:
- Google Workspace federation

LDAP:
- TrueNAS LDAP provider and outpost

CI/CD:
- GitHub Actions workflow for plan/apply
- Secrets managed via GitHub Actions secrets

Provider: beryju/authentik v2025.2

.gitignore

@@ -0,0 +1,30 @@
+# Terraform
+.terraform/
+.terraform.lock.hcl
+*.tfstate
+*.tfstate.*
+*.tfplan
+crash.log
+override.tf
+override.tf.json
+*_override.tf
+*_override.tf.json
+
+# Secrets - NEVER commit these
+*.tfvars
+!*.tfvars.example
+secrets.yaml
+secrets*.yaml
+*.pem
+*.key
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db