Add version lock ability

[sarg3nt]

First of all, just discovered huber and am LOVING it. Thank you for putting this together and keeping it up to date.

huber update will update apps installed with huber install <app> -v <version> to the latest, which is rarely the desired behavior.

Adding the ability to lock an app to a version would make huber update useful.

My primary use case is kubectl. kubectl is validated to work with one minor version of a Kubernetes cluster ahead and behind its minor version which means we need to lock kubectl to a specific minor version.

Being able to specify locks via major / minor would be ideal but I'd settle for just a version string at this point.

Possible command line examples:
huber lock kubectl v1.23.17
and
huber unlock kubectl

If you want to tackle major / minor locking then something like this might work.
huber lock kubectl v1.23.x
or huber lock kubectl v1.x.x though this makes no sense for kubectl it would for others.