reusable workflows to deploy standard cos(lite) configurations

[PietroPasotti]

Right now if a charm wants to integration test observability relations with COS, they have to figure out:

• which concierge spec to use to prepare the substrate (microk8s version, juju version...)
• how to configure the terraform plan
• update their integration testing workflows to do all of that

To help other teams/repos test against COS, reducing boilerplate, we could improve the terraform.yml and _integration.yml recipes we have on this repo to be reusable and public.

What could it look like:

# myrepo/.github/workflows/integration_tests.yaml 
jobs:
  deploy-cos:
    name: Deploy COS
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: github.com/canonical/observability-stack/deploy-cos@v1
        with: 
            cos-model: cos
            controller: cos-ctrl
    integration-tests:
    # run integration tests; now there is a microk8s controller and a cos model in it

[Abuelodelanada]

If we add a role-all minimal TF module it will likely cover most of the use-cases

[MichaelThamm]

To offer up controller and model inputs for the tester TF module we would need to add these as inputs:

• https://registry.terraform.io/providers/juju/juju/latest/docs/resources/controller
• https://registry.terraform.io/providers/juju/juju/latest/docs/resources/model

and offer those as inputs to the workflow.