improve upgrade-snaps action to better recover in error cases

[addyess]

Overview

Addresses LP#2077189
Running outside of a reconcile loop, the action will need to handle errors raised from the install method as ReconcilerErrors.

Details

• These changes promote early reconciliation failures when the install_snaps method is called and there's a condition that requires the snaps to be updated.

• Should be merged with:

  • Carefully use a status context on actions charm-kubernetes-control-plane#362
  • Don't use a status context on actions charm-kubernetes-worker#177

[kwmonroe]

+1, special thanks for considering the reconcile error that may be driven by multiple underlying problems. LGTM.