It's currently pulled from the rsvndump image but it should be explicitely defined. It's
already the case for the Dockerfile of the save-code-now apps for example.

Refs sysadm-environment#4894

Refs. swh/infra/sysadm-environment#4886

Refs. swh/infra/sysadm-environment#4792

It used to be necessary for subvertpy packaging.

This creates a new utility image holding the rsvndump pushed in the gitlab registry.

And then adapts the svn loader image to expose that new dependency tool [1]. That will
allow development to use rsvndump instead of svnrdump.

[1]
```
$ docker build -t swh-loader-svn .
$ docker run -ti --rm --user root --entrypoint rsvndump swh-loader-svn --version
rsvndump 0.6.1
Copyright (C) 2008-present Jonas Gehring <jonas@jgehring.net>
Released under the GNU General Public License.
```

Related to infra/sysadm-environment#4659

This sent celery events at the end of the ingestion which is not required. It's no
longer relevant for the current scheduling management. It's an initial typo when
migrating those workers.

Related to T4540

Related to T4540

Related to T4540