[APM] Darker shade for Error group details labels

[jim-fung]

Closes #90927

Summary

Issue 90927 was solved by changing the EUI value that is used in the header for an Error occurrence detail from theme.eui.euiColorMediumShade to theme.eui.euiColorDarkShade, thereby making it WCAG compliant.

Amount of axe accessibility issues were reduced from 13 to 11

Darkmode before/after

Lightmode before/after

Checklist

• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
  (https://github.com/elastic/kibana/blob/c29adfef29e921cc447d2a5ed06ac2047ceab552/src/dev/build/tasks/os_packages/docker_generator/resources/bin/kibana-docker)

[kibanamachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[cla-checker-service]

💚 CLA has been signed

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[dgieselaar]

@elasticmachine merge upstream

[sorenlouv]

@amtmolecule Thanks for the contribution!

[sorenlouv]

retest

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: aa40668

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
apm	5.2MB	5.2MB	-2.0B

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

[kibanamachine]

Backport result

{"level":"info","message":"POST https://api.github.com/graphql (status: 200)"}
{"level":"info","message":"POST https://api.github.com/graphql (status: 200)"}
{"meta":{"labels":["Team:apm","auto-backport","release_note:skip","v7.12.0","💝community"],"branchLabelMapping":{"^v8.0.0$":"master","^v7.12.0$":"7.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"},"existingTargetPullRequests":[]},"level":"info","message":"Inputs when calculating target branches:"}
{"meta":["7.x"],"level":"info","message":"Target branches inferred from labels:"}
{"meta":{"killed":false,"code":2,"signal":null,"cmd":"git remote rm kibanamachine","stdout":"","stderr":"error: No such remote: 'kibanamachine'\n"},"level":"info","message":"exec error 'git remote rm kibanamachine':"}
{"meta":{"killed":false,"code":2,"signal":null,"cmd":"git remote rm elastic","stdout":"","stderr":"error: No such remote: 'elastic'\n"},"level":"info","message":"exec error 'git remote rm elastic':"}
{"level":"info","message":"Backporting [{\"sourceBranch\":\"master\",\"targetBranchesFromLabels\":[\"7.x\"],\"sha\":\"5c820cc95f0ba3e6e2eb0f7461860f1dc78f87b7\",\"formattedMessage\":\"[APM] Darker shade for Error group details labels (#91349)\",\"originalMessage\":\"[APM] Darker shade for Error group details labels (#91349)\\n\\nCo-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>\",\"pullNumber\":91349,\"existingTargetPullRequests\":[]}] to 7.x"}

Backporting to 7.x:
{"level":"info","message":"Backporting via filesystem"}
{"level":"info","message":"Creating PR with title: \"[7.x] [APM] Darker shade for Error group details labels (#91349)\". kibanamachine:backport/7.x/pr-91349 -> 7.x"}
{"level":"info","message":"POST /repos/elastic/kibana/pulls - 201 in 1128ms"}
{"level":"info","message":"Adding assignees to #91393: amtmolecule"}
{"level":"info","message":"POST /repos/elastic/kibana/issues/91393/assignees - 201 in 447ms"}
{"level":"info","message":"Adding labels: backport"}
{"level":"info","message":"POST /repos/elastic/kibana/issues/91393/labels - 200 in 387ms"}
View pull request: https://github.com/elastic/kibana/pull/91393

[kibanamachine]

Looks like this PR has a backport PR but it still hasn't been merged. Please merge it ASAP to keep the branches relatively in sync.