Initial wait

**Is your feature request related to a problem? Please describe.**
Typing animations are often used to mimic human behaviour(as in chat bots). Ability to add an initial wait before the animation start would be great. Is there a built-in way to do this?

**Describe the solution you'd like**
Ability to add initial wait to text animation.
```dart
...
pause: const Duration(milliseconds: 1000),
initialPause: const Duration(milliseconds: 1000),
...
```