task(auth,graphql): Configure separate redis instance for rate limiting

[dschom]

Because

• We wanted to have a clean slate for rate limiting db state
• We've stood up a separate instance in staging

This pull request

• Adds config for a 'ratelimit' Redis instance

Issue that this pull request solves

Closes: (issue number)

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

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Other information (Optional)

Initially it seemed like we could just use the the custom's server redis instance, but ultimately decided it would be better to keep these DBs separate. There's a couple reasons for this:

• Easier to roll back
• Ensures no impact to existing customs service
• Allows us to scale individually
• Don't have to worry about old keys sticking around after fully migrating to new customs approach