CI installed vault by shelling out to `dnf install vault -y`, which reads
metadata for every enabled repo (appstream/baseos/crb/epel/ha) and downloads
the 169MB vendored vault RPM from the unkin repo on every pipeline run
(~39s per plan/apply job).
- Replace the dnf install with a pinned curl of the upstream vault zip from
the artifactapi hashicorp-releases remote proxy, extracted with python3 to
/usr/local/bin/vault.
- Pin the version via a VAULT_VERSION env var (1.20.0).