Evaluate Redis 7

Since this is an entirely new instance (redis-registry-cache), it may be cheapest to move to Redis 7 before going to production, to avoid having to do a major upgrade.

Pro:

• Saving us major version upgrade hassle
• Performance improvements (e.g. #9934)

Con:

• Drift between other redises and this one, potential BC hazard
• Additional change which increases rollout risk