fix(pivot-grid): update pinned column bindings for clarity

Author: tishko0

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-grid.component.html

@@ -6,7 +6,8 @@
     [grid]="this"
     [hasMRL]="hasColumnLayouts"
     [width]="calcWidth"
-    [pinnedColumnCollection]="pinnedColumns"
+    [pinnedStartColumnCollection]="pinnedStartColumns"
+    [pinnedEndColumnCollection]="pinnedEndColumns"
     [unpinnedColumnCollection]="unpinnedColumns"
     (keydown.meta.c)="copyHandler($event)"
     (keydown.control.c)="copyHandler($event)"