Foreign Key fixes:

1. Auto FK related fixes.
2. Properties tab not showing columns.
3. Toggle button is editable even if set to read-only.
4. Dropdown placeholder should be blank for read-only/disabled.
5. Input control help text color on a dark theme.

Fixes #6770

web/pgadmin/static/js/SchemaView/DataGridView.jsx

@@ -81,7 +81,6 @@ const useStyles = makeStyles((theme)=>({
     overflow: 'hidden',
     textOverflow: 'ellipsis',
     whiteSpace: 'nowrap',
-    textAlign: 'center',
   },
   tableCellHeader: {
     fontWeight: theme.typography.fontWeightBold,