feat: make overlays mutable

[usmanonazim]

Description

Related Ticket Currently, overlays cannot be added/removed individually - this change introduces the ability to add/remove overlays individually (customer request)

Specific Changes proposed

• New add function for adding overlays
• New remove function to remove individual overlays
• Updated docs to reflect the above changes

Requirements Checklist

• [x] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [x] Unit Tests updated or fixed
  • [x] Docs/guides updated
• [ ] Reviewed by Two Core Contributors