feat(ui5-table-selection-multi): headerSelector property added

- provides an enumeration property to switch in the multi-select case
between a select all and a clear all option
(in future further variants might be added).

Fixes: #5873

Author: aborjinik

packages/main/cypress/specs/TableSelection.cy.tsx

@@ -270,6 +270,6 @@ describe("TableSelection - Multi", () => {
 		cy.get("@headerRowCheckBox").should("have.attr", "checked");
 		cy.get("#row2").invoke("remove");
 		cy.get("#row1").invoke("remove");
-		cy.get("@headerRowCheckBox").should("not.have.attr", "checked");
+		cy.get("#headerRow").shadow().find("#selection-cell").should("not.exist");
 	});
 });