[PATCH] Enhancement in sql-field control [pgAdmin4]

Hi,

I have updated the backform control for sql-field*.*

Following are the enhancements:
1. Added border to control which was missing earlier.
2. Allows user to provide height to sql-field control by specifying
*extraClasses* field in model schema.
3. Defined new classes for sql-field control height in overrides.css
4. Added scrollbar to the control.

*Usage: *

{
id: 'definition', label:'{{ _("Definition") }}', cell: 'string',
type: 'text', mode: ['create', 'edit'], group: 'Definition',
control: *Backform.SqlFieldControl*,
*extraClasses:['custom_height_css_class']*
}

Please review the attached patch and commit if it looks good.

Thanks,
Surinder Kumar