Add token-based auth prerequisite for oc adm upgrade recommend

[asadawar]

Summary

• Adds a prerequisite to the oc adm upgrade recommend documentation noting that token-based authentication (e.g., oc login -u kubeadmin) is required
• Documents that certificate-based auth (system:admin from the installer kubeconfig) causes the command to silently skip all alert-based precondition checks
• Includes the exact error message users see so it is searchable

Context

Found during OCP 4.22 pre-GA hackathon testing of OCPSTRAT-2781. The Thanos monitoring route uses kube-rbac-proxy with TokenReview-based auth only (no --client-ca-file on port 9091), so certificate-based authentication is structurally impossible (source).

Root cause discussed with OTA maintainer (W Trevor King): The real fix belongs to the monitoring team — either providing a dedicated Thanos-access SA or adding --client-ca-file to kube-rbac-proxy-web. OTA should not hardcode SA assumptions. This doc PR is a band-aid documenting the current token requirement.

• Monitoring docs reference: Accessing monitoring APIs by using the CLI

Test plan

• Verified on OCP 4.22.0-rc.4 that system:admin produces Failed to check for at least some preconditions: no token is currently in use for this session
• Verified that oc login -u kubeadmin resolves the issue and all precheck categories are displayed
• Verified API server proxy to thanos-querier returns 401 (kube-rbac-proxy-web has no --client-ca-file)
• Verified oc create token <SA> works from cert auth but choosing the right SA is a monitoring team decision

Fixes: https://redhat.atlassian.net/browse/OSDOCS-19867

[openshift-ci]

Hi @asadawar. Thanks for your PR.

I'm waiting for a openshift member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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