Deal with Redis license changing

[robertbartel]

As discussed here (and actually executed here), Redis has changed their licensing to no longer be open source in newer versions. Opening this for deliberate tracking of subtasks to ensure DMOD remains functional, open, and license-compliant following this.

One thing worth noting at this level is that, as of this writing, the official Redis Docker image page on Dockerhub does still refer to Redis as being open source. Likely not by accident, the latest version for images is 7.2.5, which is before the licensing change (7.4).

• Pin stack config to use Redis image prior to change #640
• Ensure dmod.redis and any other DMOD usage of Redis Python package only use open-source versions
• Examine Redis forks for viable open-source alternative

[christophertubbs]

Took a look at Valkey. It should not only be a drop in replacement, but a deployment decision. It's a fork from before Redis decided to put new fancy stuff, like TimeSeries within their Redis Stack product. The python client for it is... wait for it... redis-py. i.e., what we already use. If we want a new version of Redis to solve CVEs or something, we just swap the image in the docker-compose files to that of the latest acceptable version of valkey. No problemo.

[robertbartel]

Thanks, @christophertubbs. This looks perfect. We'll go in this direction when we are ready (or are otherwise forced) to move off the current Redis image. I don't think anything compels us to do that ASAP, though I also won't argue if this gets done sooner rather than later.