feat: set metadata at the user level in CreateUser request (#11719)

# Which Problems Are Solved

Currently, metadata can be set/updated only for human users, but it
should be available also for service accounts (machine users).

# How the Problems Are Solved

This is achieved by:
- adding a metadata field at the root level in `CreateUserRequest`,
which makes it available for both `human` and `machine` user types
- returning an error when both the root level and human-level `metadata`
fields are set in the `CreateUserRequest`
- setting `human` and `machine` metadata from the root `metadata` field
in the server layer
- pushing `user.metadata.set` event during machine user creation in the
command layer
- adding integration tests

# Additional Changes
N/A

# Additional Context
- Related to https://github.com/zitadel/zitadel/issues/11369

---------

Co-authored-by: Vitor Bari Buccianti <[email protected]>
Co-authored-by: Silvan <[email protected]>

internal/command/user_machine_test.go

@@ -105,6 +105,64 @@ func TestCommandSide_AddMachine(t *testing.T) {
 				err: zerrors.IsPreconditionFailed,
 			},
 		},
+		{
+			name: "add machine with invalid metadata key, error",
+			fields: fields{
+				eventstore: eventstoreExpect(
+					t,
+				),
+				idGenerator: id_mock.NewIDGeneratorExpectIDs(t, "user1"),
+			},
+			args: args{
+				ctx: context.Background(),
+				machine: &Machine{
+					ObjectRoot: models.ObjectRoot{
+						ResourceOwner: "org1",
+					},
+					Description: "description",
+					Name:        "name",
+					Username:    "username",
+					Metadata: []*AddMetadataEntry{
+						{
+							Key:   "",
+							Value: []byte("value1"),
+						},
+					},
+				},
+			},
+			res: res{
+				err: zerrors.IsErrorInvalidArgument,
+			},
+		},
+		{
+			name: "add machine with invalid metadata value, error",
+			fields: fields{
+				eventstore: eventstoreExpect(
+					t,
+				),
+				idGenerator: id_mock.NewIDGeneratorExpectIDs(t, "user1"),
+			},
+			args: args{
+				ctx: context.Background(),
+				machine: &Machine{
+					ObjectRoot: models.ObjectRoot{
+						ResourceOwner: "org1",
+					},
+					Description: "description",
+					Name:        "name",
+					Username:    "username",
+					Metadata: []*AddMetadataEntry{
+						{
+							Key:   "key1",
+							Value: []byte(""),
+						},
+					},
+				},
+			},
+			res: res{
+				err: zerrors.IsErrorInvalidArgument,
+			},
+		},
 		{
 			name: "add machine, ok",
 			fields: fields{
@@ -131,6 +189,11 @@ func TestCommandSide_AddMachine(t *testing.T) {
 							true,
 							domain.OIDCTokenTypeBearer,
 						),
+						user.NewMetadataSetEvent(context.Background(),
+							&user.NewAggregate("user1", "org1").Aggregate,
+							"key1",
+							[]byte("value1"),
+						),
 					),
 				),
 				idGenerator: id_mock.NewIDGeneratorExpectIDs(t, "user1"),
@@ -144,6 +207,12 @@ func TestCommandSide_AddMachine(t *testing.T) {
 					Description: "description",
 					Name:        "name",
 					Username:    "username",
+					Metadata: []*AddMetadataEntry{
+						{
+							Key:   "key1",
+							Value: []byte("value1"),
+						},
+					},
 				},
 			},
 			res: res{