[App Search] Add document position indicator to Result component

[daveyholler]

Summary

Adds a result position indicator to the ResultHeader component.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

[byronhulcher]

@elasticmachine merge upstream

[byronhulcher]

Sorry for a lot of noise. I've made decision to merge as-is and created a follow-up issue to add this to the proper views once we've built those views. Thanks for building this out @daveyholler, it will merge as soon as tests pass.

[kibanamachine]

💚 Backport successful

Status	Branch	Result
✅	7.x

This backport PR will be merged automatically after passing CI.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 6dedef5
• Storybooks Preview
• Documentation Changes

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
enterpriseSearch	1.3MB	1.3MB	+316.0B

History

• 💚 Build #156058 succeeded 6dedef5
• 💚 Build #154996 succeeded 8cfc178
• 💚 Build #154789 succeeded f652196

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @daveyholler @byronhulcher