Default Redis setting causes Out of Memory crashes

### Environment

self-hosted (https://develop.sentry.dev/self-hosted/)

### Steps to Reproduce

1. Have plenty of CPU and RAM (16 cores) - 128gb
2. Have a busy server
3. Watch RAM usage by Redis climb to 70% of the total RAM
4. Other non Redis tasks tip the usage up to 100%
5. See that the OOM process clears down most of the processes
6. Find that you can't ssh on to the server, and after reboot; everything is a mess

### Expected Result

A busy server can run for multiple hours without infinity growing in RAM

### Actual Result

The busy server allows Redis to use most of the Ram, and other processes push it to 100%.

We have capped it at about 40% `redis.conf`
> maxmemory 45gb

I would suggest being able to set this as a sensible number by percentage would be great, and shipping at infinite is bad
> maxmemory 0

### Product Area

Settings

### Link

_No response_

### DSN

_No response_

### Version

25.11.1

Start with the self-hosted Redis configuration, especially redis.conf and the current maxmemory 0 setting described in the report. Review the self-hosted deployment documentation to determine how the default should be bounded or made configurable; done means a busy installation no longer allows Redis to consume unbounded memory and the setting is documented.

Written by the indexing model from the issue text.