Better document triggers docs

What does this MR do?

• Refactor the triggers page view
• Replace old images with new ones
• Mention triggers in ci/yaml/README.md

Screenshots (if relevant)

The new triggers views contains more information and is prettier :)

Before

After

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #21773 (closed)