fix: make volume optional in doc

docs/resources/server.md

@@ -269,7 +269,7 @@ resource "ionoscloud_server" "test" {
 - `licence_type` - (Optional)[string] Sets the OS type of the server.
 - `cpu_family` - (Optional)[string] CPU architecture on which server gets provisioned; not all CPU architectures are available in all datacenter regions; available CPU architectures can be retrieved from the datacenter resource. E.g.: "INTEL_SKYLAKE" or "INTEL_XEON".
 - `vm_state` - (Optional)[string] Sets the power state of the server. E.g: `RUNNING`, `SHUTOFF` or `SUSPENDED`. SUSPENDED state is only valid for cube. SHUTOFF state is only valid for enterprise.
-- `volume` - (Required) See the [Volume](volume.md) section.
+- `volume` - (Optional) See the [Volume](volume.md) section.
 - `nic` - (Optional) See the [Nic](nic.md) section.
 - `firewall` - (Optional) Allows to define firewall rules inline in the server. See the [Firewall](firewall.md) section.
 - `boot_volume` - (Computed) The associated boot volume.