Document using a local redis instead of Upstash

[Erb3]

Is your feature request related to a problem? Please describe.
When selfhosting, one may want to use a local redis instance instead of Upstash. It works flawlessly to host a redis server (or redis API compatible), and setting the UPSTASH_REDIS_REST_URL to 127.0.0.1, or the IP of the redis instance. The UPSTASH_REDIS_REST_TOKEN can be left empty, but you need to update src/env.mjs to allow the UPSTASH_REDIS_REST_TOKEN to be empty.

UPSTASH_REDIS_REST_TOKEN: z.string().min(0),

Describe the solution you'd like
I would like CONTRIBUTING.md to document the usage of a local redis instance.

Describe alternatives you've considered
A different solution would be to make redis optional, since it is only used for rate limiting. If noodle is only exposed to LAN, rate limiting is not a big concern.

Additional context
See Discord conversation about redis.

[YoussefLaunchUp]

I would love to see Redis made optional as well. Would make development easier.

[YoussefLaunchUp]

This PR has look at this plus just making it fully optional.
#333

[Erb3]

Fixed in #333