[EUI+] Missing Utilities content

[weronikaolejniczak]

The purpose of this task is to add missing content to the EUI+. docs/Utilities section

Missing content:

• Accessibility page
• Auto sizer page
• Beacon page
• Color palettes page
• Copy page
• CSS utility classes page
• Delay page
• Error boundary page
• Focus trap page
• Highlight and mark page
• HTML ID generator page
• Inner text page
• I18n page
• Mutation observer page
• Outside click detector page
• Overlay mask page
• Portal page
• Pretty duration page
• Provider page
• Resize observer page
• Scroll page
• Text diff page
• Text truncation page
• Window events page