Improve FileStorageUploadField doc

[Flaurite]

Description

Existing page: https://docs.jmix.io/jmix/flow-ui/vc/components/fileStorageUploadField.html

1. Add information that field can work without data binding.
2. Add to description to acceptedFileTypes attribute: "It also filters files in system file chooser dialog" or something like that.
3. Add description to dropAllowed attribute: "File can be dropped only on upload 'button'".
4. Add attributes:
   • css
5. Remove attributes:
   • invalid
   • requiredIndicatorVisible
6. Add elements:
   • tooltip
7. Add an example of handling events

To discuss. Consider all "...text" attributes to combine in one section with one image or images that show where the text is placed (or when).