Specify Jsonnet-Bundler Dependency Versions in Hierarchy

[srueg]

Context

Currently a component can have a jsonnetfile.json to specify Jsonnet dependencies. This file is not handled by Kapitan and therefore can't make use of the configuration hierarchy. The only way to have different versions of dependencies is with a separate branch of the component (which then can be specified in the hierarchy).

Implement a possibility to specify Jsonnet dependencies and their version in the hierarchy so they can be overridden.

For example the kube-prometheus library is specific to the K8s version and therefore needs a different version (git branch/commit) for each K8s version.

Alternatives

As described, an alternative would be to use different branches to handle this.

[srueg]

A possible solution could be to generate the jsonnetfile.json in Commodore and use input form the hierarchy to do so.

[srueg]

Implementation might affect #216

[corvus-ch]

This might also affect #173