chore: move the go code into a subfolder

apps/api/internal/command/user_v2_username.go

@@ -0,0 +1,38 @@
+package command
+
+import (
+	"context"
+
+	"github.com/zitadel/zitadel/internal/eventstore"
+	"github.com/zitadel/zitadel/internal/repository/user"
+	"github.com/zitadel/zitadel/internal/zerrors"
+)
+
+func (c *Commands) changeUsername(ctx context.Context, cmds []eventstore.Command, wm *UserV2WriteModel, userName string) ([]eventstore.Command, error) {
+	if wm.UserName == userName {
+		return cmds, nil
+	}
+	orgID := wm.ResourceOwner
+
+	domainPolicy, err := c.domainPolicyWriteModel(ctx, orgID)
+	if err != nil {
+		return cmds, zerrors.ThrowPreconditionFailed(err, "COMMAND-79pv6e1q62", "Errors.Org.DomainPolicy.NotExisting")
+	}
+
+	organizationScopedUsername, err := c.checkOrganizationScopedUsernames(ctx, orgID)
+	if err != nil {
+		return cmds, err
+	}
+
+	if err = c.userValidateDomain(ctx, orgID, userName, domainPolicy.UserLoginMustBeDomain); err != nil {
+		return cmds, err
+	}
+	return append(cmds,
+		user.NewUsernameChangedEvent(ctx, &wm.Aggregate().Aggregate,
+			wm.UserName,
+			userName,
+			domainPolicy.UserLoginMustBeDomain,
+			organizationScopedUsername,
+		),
+	), nil
+}