[UIK-2988] Start/stop button and notification in SpinContainer, Spin, Skeleton examples

[sheila-semrush]

Motivation and Context

Added start/stop button to examples of Spin, Skeleton, SpinContainer, instead of constant automatic switching.
Also added live messages on loading start/stop wherever needed.

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.