Deployment-prep has a etcd cluster but it's rather barebones and not widely used like its in production. To reduce beta-production differences (T87220), could we set it up properly on beta? The two use cases I have in mind are LVS backends ({T196662}) and database management (currently maintenance like T277070 requires someone with mediawiki deployment access and takes ages to sync across the cluster), but those likely aren't the only places where this would be useful
== Checklist
This is likely incomplete, feel free to add missing items
* [ ] Service records for etcd
* Majavah created SRV records under `svc.deployment-prep.eqiad1.wikimedia.cloud` for etcd-server-ssl, etcd, etcd.conftool.
* Not used yet, since SSL certificates do not match, WIP
* [ ] Conftool data/schema
* production has this in ops/puppet, where to put these?
* [ ] Install tooling on `deployment-cumin`?
* [ ] Use for mw databases
* [ ] Write documentation