[pgAdmin][RM4993] [Accessibility] Read-only controls and disabledcontrols needs to be separately identified

Hi Hackers,

Attached is the patch to allow input controls to be set as readonly instead of disabled.

I've also changed the code for the nodes to make sure properties tab have readonly fields wherever applicable. This will allow tab navigation in properties tab and also allow screen readers to read it.

Please note that, I've not visited each and every node create/edit dialog to identify what should be readonly or what should be disabled as it depends on business logic. The patch is mainly for the properties tab.

Kindly review.