Clarify monitoring and monitoring.collection

[karenzone]

State that both xpack.monitoring.enabled in Logstash config and xpack.monitoring.collection.enabled in Elasticsearch config are needed.

[karenzone]

@robgil @yaauie Please evaluate this approach for clarifying #9901, and let me know what you think.

[mergify[bot]]

This pull request does not have a backport label. Could you fix it @karenzone? 🙏 To fixup this pull request, you need to add the backport labels for the needed branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify[bot]]

backport-8.x has been added to help with the transition to the new branch 8.x. If you don't need it please use backport-skip label.

[mergify[bot]]

This pull request is now in conflicts. Could you fix it @karenzone? 🙏 To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b ls-9901-monitoring upstream/ls-9901-monitoring
git merge upstream/main
git push upstream ls-9901-monitoring