Add IaC support (Terraform/API) for creating Service Center services

**Why is this needed**: Grafana Service Center currently supports creating services only via the UI. There is no API or IaC resource to manage service definitions programmatically. This limits automation, reproducibility, and GitOps workflows. **What would you like to be added**: Add support for managing Service Center services through Infrastructure as Code, ideally via: 1. Terraform provider resource for IaC. 2. HTTP API for programmatic service management. **Who is this feature for?** Would allow Platform engineering, devops and SRE teams to automate and manage the Grafana service center.