Support OIDC/Federated Credential to collect Azure Metrics with serverless solution in Grafana Cloud

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: Currently, Grafana Cloud authenticates to Azure Monitor to collect Azure Metrics with serverless solution using a Service Principal with a client secret. see: https://grafana.com/docs/grafana-cloud/monitor-infrastructure/monitor-cloud-provider/azure/collect-azure-serverless/config-azure-serverless-cloudprovider/#connect-to-azure-account While effective, this approach could be optimized by leveraging EntraID Workload Identity Federation (OIDC). Using OIDC with service principals would allow Grafana Cloud to securely request short-lived tokens from Azure without storing client secrets, aligning with cloud-native authentication practices. This approach would make integrations more streamlined, secure and maintainable. **What would you like to be added**: Support for authenticating Grafana Cloud to Azure Monitor using OIDC with service principals. https://learn.microsoft.com/en-us/entra/workload-id/workload-identity-federation **Who is this feature for?** Organizations and teams using Grafana Cloud who wish to adopt cloud-native best practices for authentication, streamline serverless Azure monitoring setups, and reduce reliance on static credentials for secure and maintainable integrations.