Changes the charm from relying on a prepackaged image to
building srsue and srsenb from tagged source.
Updates the descriptor to use generic name for relation.

Signed-off-by: beierlm <mark.beierl@canonical.com>

This is are the packages used to test
the k8s proxy charm feature.

Signed-off-by: Dominik Fleischmann <dominik.fleischmann@canonical.com>

Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>