NO-JIRA: Rename Dockerfile

[ashwindasr]

Refactor name to Dockerfile.ocp as a better, version independent, alternative since contents are actually rhel9.

CI: https://github.com/openshift/release/pull/54073 (probably needs to merge first)

Please follow up with other changes in this/other repos if necessary. ART has setup the necessary fallbacks, but only for 4.17, if backporting this PR, please give us a heads up.

[openshift-ci-robot]

@ashwindasr: This pull request explicitly references no jira issue.

In response to [this](https://github.com/openshift/must-gather/pull/432): >Refactor name to `Dockerfile.ocp` as a better, version independent, alternative since contents are actually rhel9. > >CI: https://github.com/openshift/release/pull/54073 (probably needs to merge first) > >Please follow up with other changes in this/other repos if necessary. ART has setup the necessary [fallbacks](https://github.com/openshift-eng/ocp-build-data/pull/5039), but only for 4.17, if backporting this PR, please give us a heads up. Instructions for interacting with me using PR comments are available [here](https://prow.ci.openshift.org/command-help?repo=openshift%2Fmust-gather). If you have questions or suggestions related to my behavior, please file an issue against the [openshift-eng/jira-lifecycle-plugin](https://github.com/openshift-eng/jira-lifecycle-plugin/issues/new) repository.

[soltysh]

/retest now that we have https://github.com/openshift/release/pull/54073 in

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ashwindasr, soltysh

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[openshift-ci[bot]]

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