[86bzbmj36][side-panel] a11y fixes

[msereniti]

Motivation and Context

This PR fixes main issues related to side panel a11y.

1. It adds needed role to panel.
2. It makes aria-label required
3. Semantic footer and header
4. .Close and .Back are buttons with thinned paddings now.
5. Close button got localized aria-label

How has this been tested?

Manually

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue).
• [ ] New feature (non-breaking change which adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [x] Nice improve.

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly or it's not required.
• [x] Unit tests are not broken.
• [x] I have added changelog note to corresponding CHANGELOG.md file with planned publish date.
• [ ] I have added new unit tests on added of fixed functionality.

[sheila-semrush]

@j-mnizhek can you review the docs update? I updated illustrations and some width/paddings information on the Design tab, and also updated the A11y tab. You're also welcome to check out the Examples.