[UIK-2755][website] Headings and labels

[j-mnizhek]

Motivation and Context

This PR introduces changes to the headings in our documentation to conform to the '2.4.6 Headings and Labels' criterion.

1. Made small updates to the headings throughout the documentation to ensure greater consistency across documents.
2. Changed the placement of some sections to make the document structure more consistent across the documentation.

I ignored a couple of suggestions from the vale since they are not applicable for some of the changes.

How has this been tested?

Manually.

Types of changes

• 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).
• Nice improve.

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly or it's not required.
• Unit tests are not broken.
• 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.

[j-mnizhek]

Made two small updates based on our discussion on KB:

1. Replaced Location with Placement heading everywhere
2. Unified Types section. Themes sections are now included in Types section.

Also updated Pagination documentation for the other task to avoid conflicts in the structure.

[sheila-semrush]

@j-mnizhek added my own commit to avoid posting a bunch of suggestions, I've shortened some long 2nd level headings and unified example headings a bit, feel free to add or edit over it

[j-mnizhek]

@j-mnizhek added my own commit to avoid posting a bunch of suggestions, I've shortened some long 2nd level headings and unified example headings a bit, feel free to add or edit over it

Decided to move all the things related to appearance under the Appearance section, so that in the future we wouldn’t have to think much when we should put sizes, types, and topics outside of it, and where we shouldn’t.

[j-mnizhek]

@sheila-semrush Made small updates, added missed Appearance headings, fixed dead link (it's strange that only one was found).

[sheila-semrush]

@j-mnizhek looks good to me!
You can also look at my last commit, I thought we need to fix the heading structure in our README/CONTRIBUTING files, so that the overall structure is correct when you view them on Github. Feel free to edit If you have any suggestions.