[Observability] Add side navigation for serverless observability

[kpatticha]

Summary

The PR introduces the first iteration of the side navigation bar for serverless observability. Part of #153777

Run locally

yarn serverless-oblt

Screenshots

Screen.Recording.2023-05-11.at.13.41.02.mov

Fixes

• Fix rendering the icon for the nested navigation items
  • 24ee4dc

Notes

• There is an issue where the selected navigation item is not properly highlighted and loses focus when the user clicks anywhere else on the page. (atm out of the scope of the PR)
• The navigation tree is subject to change as there is an ongoing discussion about the naming and order

[apmmachine]

🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[tsullivan]

Small change requested to use the serverless plugin for setting the side nav

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: aebe5f9

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
serverlessObservability	4	28	+24

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
serverlessObservability	1.5KB	21.1KB	+19.5KB
serverlessSearch	23.2KB	23.3KB	+66.0B
total			+19.6KB

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
securitySolution	400	404	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
securitySolution	480	484	+4
total			+6

History

• 💚 Build #127109 succeeded a80f557
• 💚 Build #127056 succeeded c7f48a3

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

[tsullivan]

LGTM