[EuiPageTemplate] Add new EuiPageTemplate.TopBar component for serverless navigation

[cee-chen]

Summary

closes #7765

⚠️ TODOS:

• Figure out child API for links? leave it flexible or try to make it opinionated? need to figure out what layouts are being used by Kibana solutions
• Documentation

QA

• https://eui.elastic.co/pr_7777/storybook/?path=/story/templates-euipagetemplate--playground
• https://eui.elastic.co/pr_7777/storybook/?path=/story/navigation-euicollapsiblenav-beta-kibanasolution--playground

General checklist

• Browser QA
  • Checked in both light and dark modes
  • Checked in mobile
  • Checked in Chrome, Safari, Edge, and Firefox
    - [ ] Checked for accessibility including keyboard-only and screenreader modes
• Docs site QA
  • Added documentation
  • Props have proper autodocs (using @default if default values are missing) and playground toggles
    - [ ] Checked Code Sandbox works for any docs examples
• Code quality checklist
  • Added or updated jest and cypress tests
• Release checklist
  • A changelog entry exists and is marked appropriately.
    - [ ] If applicable, added the breaking change issue label (and filled out the breaking change checklist)
• Designer checklist
  • Updated the Figma library counterpart

[kibanamachine]

Preview staging links for this PR:

• Docs site: https://eui.elastic.co/pr_7777/
• Storybook: https://eui.elastic.co/pr_7777/storybook

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: f18958f

[cee-chen]

@MichaelMarcialis @ryankeairns FYI that I'll probably ping you two about this work and try to schedule a call / chat about what kind of content should go into this top bar.

[cee-chen]

Quick TL;DR from our team sync with Marcialis today - 99.9% of design cases should have either left-side or right-side icons, so we could consider implementing an API similar to EuiHeader's sections or items props. Or we could always just leave a wildcard children to be rendered and let Kibana determine what to render in this top bar.

I might pull in @tsullivan at this point to discuss preferred API for content, since I believe he's implemented something similar in Kibana.

[cee-chen]

Closing, Kibana has resolved this within their own repo.