[Docs] Add more examples to the `Form` page

[Form page](https://uui.epam.com/documents?id=form).

Proposed examples:
1. Validation of array fields
* **Example**: I have a record with an array field, that contains reported hours per day (that are mapped to `NumericInput` controls), and I want to validate that at least one of them is filled in (not `null` or greater than 0)
2. Validation of multiple records
* **Example**: I have several records with start time and end time values (that are mapped to `TimePicker` controls), and I want to validate that the periods in the records do not overlap. A validation error message should be displayed for each problematic record
3. Validation without connection to a particular input (global error)
* **Example**: I have several records like in point 1, and I want to validate, that on each day the sum of hours is less than or equal to 24 hours. A validation error message can be displayed in a modal window's footer or other places
* On the one hand, it could be moved out and handled manually by users, but on the other hand, it would be convenient to keep things in one place and follow the form's settings (like `validateOn` strategy) instead of synchronizing manual and the form's code
4. One error message and multiple highlighted inputs per record
* **Example**: The same as in point 2, and I want to display a single message per record while highlighting both start time and end time controls

It is possible, that it will be necessary to improve the form's code before providing the examples.