Docs: Missing information in BlockUI's docs related to BlockableUI interface.

[qwadrox]

Describe the bug

The docs should mention that target of BlockUI must implement BlockableUI interface when it's a custom Component.

Environment

Reproducer

No response

Angular version

18.0.1

PrimeNG version

17.18.9

Build / Runtime

Angular CLI App

Language

TypeScript

Node version (for AoT issues node --version)

Browser(s)

No response

Steps to reproduce the behavior

No response

Expected behavior

No response