Add charmcraft.yaml debug_mode to charmed-osm

- Added a debug_mode option to lcm, mon, nbi, pol, and ro charms
- Added a script to prepare pods for debugging:
  - setup .ssh/config to easily ssh from vscode to the pods
- Added a README that explains how to prepare the environment for
testing

Change-Id: Ieb56b565c15e61c68ad000b60897abd27e1eeb0e
Signed-off-by: David Garcia <david.garcia@canonical.com>