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 multiple-charm repo.

Removed files:

• cd.yaml - this is covered by the publish action