docs: Remove the need for adding a Quay token as a global pull secret in the RHDH CI install procedure

[rm3l]

Description

This is no longer needed since the rhdh organization is public on Quay.

Which issue(s) does this PR fix or relate to

—

PR acceptance criteria

• [ ] Tests
• [x] Documentation
• [ ] If the bundle manifests have been updated, make sure to review the rhdh-operator.csv.yaml file accordingly

How to test changes / Special notes to the reviewer

Just run .rhdh/scripts/install-rhdh-catalog-source.sh --latest --install-operator rhdh, and the operator should be installed without any need for adding your Quay token as a global pull secret in OCP.

[openshift-ci[bot]]

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