Update rsyslog.md

[estherk15]

What does this PR do? What is the motivation?

• Documentation feedback to remove outdated configuration information: https://github.com/DataDog/documentation/issues/22150

• Added a note instead of removing, since the current configuration is also used as an example in the Rsyslog docs.

• Added note that omhttp needs to be installed for US5: https://datadoghq.atlassian.net/browse/DOCS-8445

  Merge instructions

• Pending approval from Logs team

Additional notes

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/esther/docs-7422-add-rsyslog-note/integrations/rsyslog