CMP-2688: Document using relatedImages for must-gather

[rhmdnd]

Even though we documented using an image directly for must-gather support, we can also include the relatedImages reference in the usage guide.

[openshift-ci-robot]

@rhmdnd: This pull request references CMP-2688 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the sub-task to target the "4.17.0" version, but no target version was set.

In response to [this](https://github.com/ComplianceAsCode/compliance-operator/pull/542): >Even though we documented using an image directly for must-gather support, we can also include the relatedImages reference in the usage guide. Instructions for interacting with me using PR comments are available [here](https://prow.ci.openshift.org/command-help?repo=ComplianceAsCode%2Fcompliance-operator). 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.

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rhmdnd

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/ComplianceAsCode/compliance-operator/blob/master/OWNERS)~~ [rhmdnd] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[github-actions[bot]]

:robot: To deploy this PR, run the following command:

make catalog-deploy CATALOG_IMG=ghcr.io/complianceascode/compliance-operator-catalog:542

[BhargaviGudi]

/lgtm