[APM] Add missing settings to documentation

[bmorelli25]

Summary

This PR adds missing APM/Observability settings to the documentation:

• observability:apmAgentExplorerView
• observability:apmAWSLambdaPriceFactor
• observability:apmAWSLambdaRequestCostPerMillion
• observability:apmEnableContinuousRollups
• observability:apmEnableServiceMetrics
• observability:apmLabsButton
• observability:apmServiceGroupMaxNumberOfServices
• observability:apmDefaultServiceEnvironment

This PR also adds @elastic/obs-docs as a codeowner to /x-pack/plugins/observability/server/ui_settings.ts so that we don't miss documenting settings moving forward.

Closes #118795.

[github-actions]

Documentation preview:

• ✨ Changed pages

[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!)

[elasticmachine]

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

[bmorelli25]

@cauemarcondes what does this config do? I couldn't figure it out.

[sorenlouv]

It's used to calculate the cost running on serverless:

kibana/x-pack/plugins/apm/server/routes/metrics/serverless/helper.ts

Lines 90 to 92 in 5fca22a

	const estimatedCost =
	computeUsageGbSec * priceFactor +
	transactionThroughput * (awsLambdaRequestCostPerMillion / 1000000);

The price is the number of requests (throughput) multipled with the AWS Lambda request cost (currently the monthly request price is $0.20 per one million request)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 69c5c20

Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	14	16	+2
securitySolution	411	415	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	15	17	+2
securitySolution	490	494	+4
total			+6

History

• 💚 Build #141760 succeeded 9024ffe
• 💚 Build #141443 succeeded 70a82de

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

cc @bmorelli25

[kibanamachine]

💔 All backports failed

Status	Branch	Result
❌	8.8	Backport failed because of merge conflicts You might need to backport the following PRs to 8.8: - Clarify documentation for the observability:enableComparisonByDefault setting (#161372) - [APM] Documentation updates (#160951)
❌	8.9	Backport failed because of merge conflicts You might need to backport the following PRs to 8.9: - [Security Solution] Update insight depth limit to 1 (#161901)

Manual backport

To create the backport manually run:

node scripts/backport --pr 161603

Questions ?

Please refer to the Backport tool documentation

[bmorelli25]

Backported manually in #161925 and #161926

[kibanamachine]

Friendly reminder: Looks like this PR hasn’t been backported yet.
To create automatically backports add the label auto-backport or prevent reminders by adding the backport:skip label.
You can also create backports manually by running node scripts/backport --pr 161603 locally