fix: user metadata check if already existing (#10430)

# Which Problems Are Solved

If metadata is set, there is no check if it even has to be changed.

# How the Problems Are Solved

Check if metadata already exists, and push no event if nothing changed.

# Additional Changes

Original changes under #10246 amendet for v3.3.x, removed permission
check
Fixes #10434

# Additional Context

none

---------

Co-authored-by: Gayathri Vijayan <66356931+grvijayan@users.noreply.github.com>
Co-authored-by: Marco A. <marco@zitadel.com>
Co-authored-by: Tim Möhlmann <tim+github@zitadel.com>

internal/command/project_member.go

@@ -45,7 +45,7 @@ func (c *Commands) addProjectMember(ctx context.Context, projectAgg *eventstore.
 		return nil, zerrors.ThrowInvalidArgument(nil, "PROJECT-3m9ds", "Errors.Project.Member.Invalid")
 	}
 
-	err = c.checkUserExists(ctx, addedMember.UserID, "")
+	_, err = c.checkUserExists(ctx, addedMember.UserID, "")
 	if err != nil {
 		return nil, err
 	}