Docs: Create the new Infra nav on the docs site (higher level)
Proposal
Follows gitlab#337297 (closed).
Create the new nav on the docs site (higher level):
.
+-- Manage your infrastructure
| +-- IaC
| +-- Terraform integrations
| +-- Terraform state
| +-- Kubernetes clusters
| +-- Connect your cluster
| +-- Agent
| +-- Manage your cluster
| +-- Deploy to your cluster
| +-- Runbooks
ETA %14.3
Who can address the issue
@marcia and the ~"devops::configure" team.