Feature: Activity Input Validation

### 🚀 Feature Request

**Context**: Activity inputs play a crucial role in workflow functionality, and invalid or unexpected inputs can lead to runtime errors or unpredictable behavior.

### Feature Description:
It would be greatly beneficial to introduce a validation layer for activity inputs in Elsa Studio. This would not only help in reducing the number of erroneous workflows but also provide instant feedback to the user, improving the overall user experience.

#### Proposed solution:
- Leverage MudBlazor's form input validation.
- Define validation rules for standard activities out of the box.
- Allow custom activity developers to specify their own validation rules.
- Provide clear error messages and visual cues in the UI for inputs that don’t meet the validation criteria.