feat: add option to lock page, variable binding

[olliethedev]

Changes in this PR:

• add prop to ui builder component to disable adding and removing pages
• add options to registry to allow for providing default locked binding

Use cases:

• when using UI-Builder to edit specific pages (ex. only edit profile page)
• when data variables are decided by business logic (ex. email template editor, where variable is bound to email recipient's first name)