Add charming actions

[natalian98]

Charming actions updated according to the ones agreed on template-operator charm.
The aim was to:

• add release charm action

• have two publish actions for on: push and on: pull_request:

  • on pull_request, publish to branch no matter if tests passed (tests and publish should run simultaneously)
  • on push, publish to latest/edge only if tests passed

• avoid re-running the tests on pull_request

• use reusable workflows in order to avoid duplication of code.

Note: this is a single-charm repo with one resource.

[github-actions]

Libraries are not up to date with their remote counterparts. If this was
not intentional, run charmcraft fetch-libs and commit the updated libs
to your PR branch.

stdout

Library charms.grafana_k8s.v0.grafana_dashboard updated to version 0.11.       
Library charms.prometheus_k8s.v0.prometheus_scrape updated to version 0.19.    

stderr