Add and delete fields in the tuple via update_fields command

1. Extend SET(field_no, value) operation in UPDATE_FIELDS command:
    - if field_no is within tuple->cardinality, it works as before, assigning the field at the given index
    - when field_no == cardinality, a new field is appended to the end of the tuple
    - if field_no > cardinality, an error is returned (ER_NO_SUCH_FIELD)
2. Add new remove operation to update_fields command. This operation should be delete a field from the tuple given field index.