Change default downstream packaging suffix to `+apertisX`

We moved from `coX` to `apertisX` as the packaging suffix but
unfortunately it turned out to interact badly with the build suffix on
OBS in some scenarios:

1. `bluez` in Debian has the `5.55-3` version
2. it gets uploaded to OBS with no changes, forgetting to add the
   `apertisX` suffix
3. OBS appends the build suffix, generating binaries with version
   `5.55-3bv2022dev2b1`
4. we update `bluez` appending the `apertisX` suffix, yielding
   `5.55-3apertis1`
5. OBS appends the build suffix, generating binaries with version
   `5.55-3apertis1bv2022dev2b1`
6. reprepro gets the new binaries from OBS but the ordering is now wrong
   since `5.55-3apertis1bv2022dev2b1` < `5.55-3bv2022dev2b1` and will
   refuse to publish the newly built binaries

Switching to `+apertisX` has the following advantages:

* it can be rolled out progressively using the standard workflow
* no need to change the build suffix
  * no need to rebuild everything on OBS
  * no need to manually delete entries from reprepro
* backports work correctly, `+apertisX` sorts newer than `coX` and
  the OBS suffixes
* mixing releases like v2021 and v2022 should not produce surprising
  effects like v2021 builds sorting newer than v2022

The drawbacks are:
* every non-Apertis-specific package needs to be tweaked
* if Debian package maintainer releases a new version by appending a
  suffix there are higher chances that the `+apertisX` suffix will sort
  newer (we already have this issue, but this increases the chances to
  hit it)

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>