Allow to specify version for Alpine
Alpine releases are supported for 2 years. Allow to specify what version do you want to generate the image for.
As @bentiss suggested, keeping FDO_DISTRIBUTION_VERSION: latest
in .fdo.alpine acts as a default value, used if the user does not specify its own FDO_DISTRIBUTION_VERSION. A small change in the template was needed to achieve that, and as a result, now a default version can be specified for any distro, not only for Alpine. This MR only sets it for Alpine, though.
Tested here: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/pipelines/1278964 (note: alpine:default_version
is a CI job that doesn't define FDO_DISTRIBUTION_VERSION, so the default value is used).
Fixes: #71 (closed)