add a 30s cache on redis

[jimfangx]

inspiration from: https://github.com/benborgers/opensheet

https://github.com/benborgers/opensheet/blob/main/index.js#L95-L97

30s might cut repeated latency in half for requests that are not update sensitive (ex: whats on the front page)

redis prob better than mongo for this

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cache on front page stuff: 5 min?
cache on user data /me - 1 min? 2 min?
cache on time sensitive user data - 30s?