Update docs for ListItem, update multivalue taxonomy field of a file list item

[kotsiossp97]

Category

• [ ] Bug fix?
• [ ] New feature?
• [ ] New sample?
• [x] Documentation update?

What's in this Pull Request?

Updated documentation for updating a multi-value taxonomy field for a file list item. As observed, a different serialization for the field values is needed.

[patrick-rodgers]

Thank you!