[#2295] `VaDataTable` scroll events

[RVitaly1978]

Description

close #2295

changes:

• [x] add prop scrollEventsThreshold (type number)
• [x] add scroll:bottom and scroll:top emits
• [x] update docs example

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)