Set up Grafana Mimir multi-tenancy and configure remote_write from multiple Prometheus instances to separate tenant namespaces

Steps

1. Deploy Grafana Mimir in microservices mode (for production) or monolithic mode (for evaluation) using the official Helm chart; configure a shared object store backend (S3, GCS, or Azure Blob) in the mimir.yaml config
2. Enable multi-tenancy by setting multitenancy_enabled: true in mimir.yaml; Mimir then requires all requests to carry an X-Scope-OrgID header to identify the tenant
3. Configure each Prometheus instance's remote_write block with the Mimir /api/v1/push endpoint URL and set headers: X-Scope-OrgID: <tenant-id> to namespace metrics by tenant
4. Grant tenants access by configuring per-tenant limits in the overrides section of mimir.yaml; set max_global_series_per_user, ingestion_rate, and other quotas per tenant as needed
5. Query tenant-specific data in Grafana by adding a Prometheus data source pointing at Mimir's query-frontend URL and setting the X-Scope-OrgID header in the data source custom HTTP headers
6. Monitor ingestion health per tenant using Mimir's built-in dashboards (importable from the Mimir mixin) which show per-tenant series counts, ingestion rates, and query latencies