Redis role in Quay architecture

This is a bug affecting Quay documentation.

Redis has always been considered a non-critical component since it stores live builder logs and the Quay tutorial according to the documentation.

The reality is that Redis is a key component for Quay because it is also used for the locking mechanism used by the garbage collector.
If there is any issue with Redis, the GC will stop working properly.

We should clarify that Redis is not only used for builder logs and the tutorial.

References to Redis in the documentation:

• https://access.redhat.com/documentation/en-us/red_hat_quay/3/html/deploy_red_hat_quay_-_high_availability/poc-overview#poc-external-components
• https://access.redhat.com/documentation/en-us/red_hat_quay/3/html/deploy_red_hat_quay_for_proof-of-concept_non-production_purposes/poc-overview#poc-external-components
• https://access.redhat.com/documentation/en-us/red_hat_quay/3/html/deploy_red_hat_quay_on_openshift_with_the_quay_operator/operator-concepts#operator-components-managed