Dependencies that exist solely for the Percona PostgreSQL binary
tarballs (the simpleimage builds in ppg:staging:NN:tarballs) and are
PG-version-agnostic, so every PG major's tarball project consumes this
one subproject:

- /opt-prefixed runtimes bundled into the artifact (percona-perl,
percona-tcl, percona-python3, percona-gdal, percona-proj): every
path compiled to /opt so the RPM-built PLs/PostGIS resolve them with
zero environment variables.
- EL8-only portability rebuilds whose libraries the ssl1.1 tarball
bundles (krb5 with builtin crypto, libssh with the libgcrypt
backend): no RHEL-OpenSSL-1.1-fork symbol nodes.
- percona-gis-compat: payload-free shim providing the distro GDAL/PROJ
package NAMES PostGIS requires by name, so image expansion has a
choice that `Prefer: percona-gis-compat` resolves (prjconf Ignore:
is not applied to image-type recipes). Its fake Provides stay
invisible outside the tarball chroots: only the ssl* repos path this
project.

percona-psql is the one tarball-only helper NOT here: it is built from
the PG source of each major (PG-version-bound _service revision), so
it lives in each ppg:staging:NN:tarballs project.

Repos mirror ppg:common:deps' Rocky repos — one per tarball EL base:
RockyLinux_8 (ssl1.1), RockyLinux_9.6 (ssl3, the RHEL 9.6 EUS vault),
RockyLinux_9 (ssl3.5, rolling 9.8+). Never published: consumed only
through the tarball projects' repository paths. No project-config of
its own — the root prjconf (inherited) already carries the EL8
libverto-libev and EL9/9.6 Prefer blocks these packages need.