[enterprise-4.15] OBSDOCS-813: Update rhobs/prometheus-example-app version in monitoring docs to 0.4.2

[openshift-cherrypick-robot]

This is an automated cherry-pick of #71344

/assign bburt-rh

[openshift-ci-robot]

@openshift-cherrypick-robot: Ignoring requests to cherry-pick non-bug issues: OBSDOCS-813

In response to this:

This is an automated cherry-pick of #71344

/assign bburt-rh

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[ocpdocs-previewbot]

🤖 Fri Feb 09 14:27:21 - Prow CI generated the docs preview: https://71424--ocpdocs-pr.netlify.app

[openshift-ci]

@openshift-cherrypick-robot: all tests passed!

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