fix(cluster): add min_nodes validation to v1 schema and improve error messages

- Add ValidateDiagFunc to min_nodes in cluster_v1 schema to match the
  validation in the current schema (>= 3 and divisible by 3)
- Improve multi-datacenter error messages to be more descriptive by
  including context about what was found

These changes ensure consistent validation during state migration and
provide clearer error messages for users.

Author: adambabik

internal/provider/cluster/cluster.go

@@ -360,7 +360,7 @@ func resourceClusterRead(ctx context.Context, d *schema.ResourceData, meta inter
 	}
 
 	if n := len(cluster.Datacenters); n > 1 {
-		return diag.Errorf("multi-datacenter clusters are not currently supported: %d", n)
+		return diag.Errorf("multi-datacenter clusters are not currently supported (found %d datacenters)", n)
 	}
 
 	var instanceExternalID string
@@ -488,7 +488,7 @@ func resourceClusterUpdate(ctx context.Context, d *schema.ResourceData, meta int
 	}
 
 	if n := len(cluster.Datacenters); n > 1 {
-		return diag.Errorf("multi-datacenter clusters are not currently supported: %d", n)
+		return diag.Errorf("multi-datacenter clusters are not currently supported (found %d datacenters)", n)
 	}
 
 	// Resize will fail if there is any ongoing cluster request.

internal/provider/cluster/cluster_v1.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/hashicorp/go-cty/cty"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
 )
 
@@ -113,6 +115,16 @@ func resourceClusterV1() *schema.Resource {
 			"min_nodes": {
 				Required: true,
 				Type:     schema.TypeInt,
+				ValidateDiagFunc: func(v interface{}, path cty.Path) diag.Diagnostics {
+					value := v.(int)
+					if value < 3 {
+						return diag.Errorf("min_nodes must be at least 3, got %d", value)
+					}
+					if value%3 != 0 {
+						return diag.Errorf("min_nodes must be divisible by 3, got %d", value)
+					}
+					return nil
+				},
 			},
 		},
 	}