[7.x] [APM] Visual improvements for new APM layout with left navigation (#101360)

[kibanamachine]

Backports the following commits to 7.x:

• [APM] Visual improvements for new APM layout with left navigation ([APM] Visual improvements for new APM layout with left navigation #101360)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: a10792b
• Storybooks Preview

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
apm	1600	1599	-1

Async chunks

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

id	before	after	diff
apm	4.3MB	4.3MB	+102.0B

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

cc @sqren