Batou-ext

- Nothing changed yet.

- oci: make `useruid.service` wait until all containers have exited and clear `/tmp` of containers.
Without those, unclean shutdowns were observed that prevented the containers from getting back
up on a reboot.

- Add a new parameter for `nix.UserEnv` components to ignore collisions between file names from different derivations or outputs of the same derivation

- `batou_ext.oci.Container`: set `backend` explicitly in Nix expression.

Otherwise this depends on the state version having varying results depending on whether
the machine was installed with a NixOS older or newer than 22.05.

- `batou_ext.oci.Container`: allow to use `podman` as backend instead of `docker`.
This also enables the following features:

* Rootless containers: by setting the `user` option to a different user. By default,
the service user of the deployment is used.

* Only mark services as `active` if the container is up. This requires that the
container has a healthcheck. Alternatively, a healthcheck can be configured
with the health_cmd attribute.

- `batou_ext.file.SymlinkAndCleanup`: add option `etag_suffix`.
This contains a suffix that each symlinked file may have.

For instance, when doing `SymlinkAndCleanup` on a file downloaded with
`batou_ext.s3.Download`, the pattern `*.tar.gz` doesn't clean up the
`.etag` files. However, `*.tar.gz*` (or an equivalent) would also remove
the etag files of the files that are symlinked to `current` & `last`.