SOLR build management confusing

[jbrown-xentity]

We typically use latest for all our builds, but we aren't for SOLR.

How to reproduce

We are currently using 8-stunnel-root as the tag for production, and is hardcoded into our development process:

https://github.com/GSA/catalog.data.gov/blob/main/docker-compose.yml#L33C3-L44C15

Expected behavior

Using latest tag

Actual behavior

Using 8-stunnel-root tag

Sketch

@FuhuXia noted that SOLR shouldn't be getting lots of updates as it can be unstable; we should probably turn this into a formal stable tag and leave it alone. We should formalize a way to manage the stable tag, in case it needs updating from latest. Or take it out of CI/CD entirely, rename the current one in use to stable, and make it a manual push always.