Expose the currently active MetalK8s version behind a symbolic link

[gdemonet]

To simplify automation and documentation of projects running on MetalK8s, it could be useful to provide a symbolic link to the mountpoint of the currently "active" version (same version as the metalk8s.scality.com/cluster-version annotation on the kube-system Namespace).

Projects could reference scripts using the symlink /srv/scality/metalk8s, which would resolve to /srv/scality/metalk8s-{{current_version}}:

# Add a new archive
/srv/scality/metalk8s/solutions.sh import --archive /path/to/my-archive.iso

# Activate this new archive
/srv/scality/metalk8s/solutions.sh activate --name my-solution --version 1.0.0

Such symlink could also be referenced in our own documentation, if desired. We could even imagine building "shim" scripts which can infer the desired version of a script to use depending on context. Take a metalk8s-upgrade shim:

• it would read the destination-version argument, and try to find the corresponding version in the available mounted ISOs
• if no such argument is provided, it would use the highest mounted version and upgrade from there

Many things are possible, but a first step to expose the current version would already make things simpler for admins trying to manage Solutions.

[NicolasT]

Not sure I'm super fond of this idea. It would require for us to be very sure we always keep that symlink 'correct' at all times. Especially on the second part, the upgrade script which 'magically' picks some version to upgrade to, I believe is dangerous. Better be explicit. It means one has to type a destination version (big deal!), but at least removes a bunch of potential surprises.

[gdemonet]

Agreed, that was my first concern as well.
I think building "shim" scripts which would check this version at runtime makes more sense than a symlink, actually.
As for upgrade, we could enforce that the shim requires a destination version argument.