Extend mariadb_instance docs for monitoring_instance_id (#662)

Author: marceljk

docs/resources/mariadb_instance.md

@@ -59,6 +59,6 @@ Optional:
 - `max_disk_threshold` (Number) The maximum disk threshold in MB. If the disk usage exceeds this threshold, the instance will be stopped.
 - `metrics_frequency` (Number) The frequency in seconds at which metrics are emitted.
 - `metrics_prefix` (String) The prefix for the metrics. Could be useful when using Graphite monitoring to prefix the metrics with a certain value, like an API key
-- `monitoring_instance_id` (String) The ID of the STACKIT monitoring instance.
+- `monitoring_instance_id` (String) The ID of the STACKIT monitoring instance. Monitoring instances with the plan "Observability-Monitoring-Starter" are not supported.
 - `sgw_acl` (String) Comma separated list of IP networks in CIDR notation which are allowed to access this instance.
 - `syslog` (List of String) List of syslog servers to send logs to.

stackit/internal/services/mariadb/instance/resource.go

@@ -146,7 +146,7 @@ func (r *instanceResource) Schema(_ context.Context, _ resource.SchemaRequest, r
 		"max_disk_threshold":     "The maximum disk threshold in MB. If the disk usage exceeds this threshold, the instance will be stopped.",
 		"metrics_frequency":      "The frequency in seconds at which metrics are emitted.",
 		"metrics_prefix":         "The prefix for the metrics. Could be useful when using Graphite monitoring to prefix the metrics with a certain value, like an API key",
-		"monitoring_instance_id": "The ID of the STACKIT monitoring instance.",
+		"monitoring_instance_id": "The ID of the STACKIT monitoring instance. Monitoring instances with the plan \"Observability-Monitoring-Starter\" are not supported.",
 		"syslog":                 "List of syslog servers to send logs to.",
 	}