Update item Edit polygon, Settings and Workspace in User Guide

[TOsmanov]

Motivation and context

This PR contains update item Edit polygon, Settings, Workspace in user_guide.md and update images.
This PR will solve the problem of #3028 and add information of #3017.

Resolved #3028

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[coveralls]

Coverage remained the same at 74.936% when pulling 44557fd on TOsmanov:UG-update-item-edit-polygon into 4b743d7 on openvinotoolkit:develop.