OSDOCS 11250: Added securing routes with externally managed certificate section in cert-manager

[subhtk]

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Version(s): 4.16

Issue: https://issues.redhat.com/browse/OSDOCS-11250

Link to docs preview: https://78502--ocpdocs-pr.netlify.app/openshift-enterprise/latest/security/cert_manager_operator/cert-manager-securing-routes.html

QE review:

• [ ] QE has approved this change.

Additional information:

[ocpdocs-previewbot]

🤖 Thu Jul 04 14:54:56 - Prow CI generated the docs preview:

https://78502--ocpdocs-pr.netlify.app/openshift-enterprise/latest/security/cert_manager_operator/cert-manager-securing-routes.html

[openshift-ci[bot]]

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