[#979] adm/subnet: Add commands to add/remove nodes

Implement `ManageNodes` operation on morph subnet client.
 Add `node add` and `node remove` commands to `subnet` section.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/morph/client/subnet/nodes.go

@@ -0,0 +1,54 @@
+package morphsubnet
+
+import "github.com/nspcc-dev/neofs-node/pkg/morph/client"
+
+// ManageNodesPrm groups parameters of node management in Subnet contract.
+//
+// Zero value adds node to subnet. Subnet and node IDs must be specified via setters.
+type ManageNodesPrm struct {
+	// remove or add node
+	rm bool
+
+	args [2]interface{}
+}
+
+// SetRemove marks node to be removed. By default, node is added.
+func (x *ManageNodesPrm) SetRemove() {
+	x.rm = true
+}
+
+// SetSubnet sets identifier of the subnet in a binary NeoFS API protocol format.
+func (x *ManageNodesPrm) SetSubnet(id []byte) {
+	x.args[0] = id
+}
+
+// SetNode sets node's public key in a binary format.
+func (x *ManageNodesPrm) SetNode(id []byte) {
+	x.args[1] = id
+}
+
+// ManageNodesRes groups resulting values of node management methods of Subnet contract.
+type ManageNodesRes struct{}
+
+// ManageNodes manages node list of the NeoFS subnet through Subnet contract calls.
+func (x Client) ManageNodes(prm ManageNodesPrm) (*ManageNodesRes, error) {
+	var method string
+
+	if prm.rm {
+		method = "removeNode"
+	} else {
+		method = "addNode"
+	}
+
+	var prmInvoke client.InvokePrm
+
+	prmInvoke.SetMethod(method)
+	prmInvoke.SetArgs(prm.args[:]...)
+
+	err := x.client.Invoke(prmInvoke)
+	if err != nil {
+		return nil, err
+	}
+
+	return new(ManageNodesRes), nil
+}