Added check all nulls to modify column Page (#10683) (#10751)

* -Added check all null checkbox

* Modified declarative table to add check all columns  in the column header

* -changed to using existing methods for firing events.

* -changed table height to auto
-center aligned data in table cell
-Check all generates event for only changed values

* -changes column header from text to column header (#10787)

* This fixes the weird angular stuff - we need to do this in every other component

* -added changes made by amir for dom object tracking
-added automatic checkall detection.
-made text-align center in table cells

* -fixed styling issues and issue with checkboxes

* -Removed unsued function

Co-authored-by: Amir Omidi <amomidi@microsoft.com>

extensions/import/src/wizard/api/models.ts

@@ -30,3 +30,5 @@ export interface ColumnMetadata {
 	primaryKey: boolean;
 	nullable: boolean;
 }
+
+export type ColumnMetadataArray = (string | number | boolean)[];