fix: Docs and Terraform usage after cutting track/2

[MichaelThamm]

Issue

After we created a track/2 branch, we now support deploying our TF product modules from dev/risk and 2/risk. This also means we need to maintain the docs, tests, and modules separately across branches.

When upgrading from 2/stable to dev/edge, Grafana refreshes to rev174, and fails:

Added charm-hub charm "grafana-k8s", revision 174 in channel dev/edge, to the model
ERROR updating charm config: cannot upgrade application "grafana" to charm "ch:amd64/grafana-k8s-174": would break relation "grafana:ingress traefik:traefik-route"

This is due to Grafana having a new ingress interface. We need to:

1. Remove the relation
2. Re-relate

Tip

Breaking backwards compatability in our TF modules, e.g. upgrading an interface, also disables the use of Terraform to upgrade our product. Related:

• Refreshing a charm's channel does not upgrade its revision to latest in channel juju/terraform-provider-juju#967

Solution

This PR has main as the merge target with these changes:

1. Update the docs to deploy from 2/stable with TF module sourced from ?ref=track/2
2. Remove integration tests deploying from channel=1/stable since we don't support a track 1 deployment
3. Fix integration tests to correctly deploy from track/2
4. Add upgrade tests from 2/stable to dev/edge

Checklist

• I have added or updated relevant documentation.
• PR title makes an appropriate release note and follows conventional commits syntax.
• Merge target is the correct branch, and relevant tandem backport PRs opened.

Context

Testing Instructions

The goal of this testing is to ensure that the module can fully deploy without Client Error.

COS Lite

module "cos-lite" {
  source = "git::https://github.com/canonical/observability-stack//terraform/cos-lite"
  model_uuid                      = juju_model.cos-lite.uuid
  channel                         = "dev/edge"
  internal_tls                    = "false"
}

Apply complete! Resources: 34 added, 0 changed, 0 destroyed.

COS

module "cos" {
  source = "git::https://github.com/canonical/observability-stack//terraform/cos"
  model_uuid                      = juju_model.cos.uuid
  channel                         = "dev/edge"
  internal_tls                    = false

  s3_endpoint   = "http://10.1.185.11:8333"
  s3_secret_key = "placeholder"
  s3_access_key = "placeholder"

  loki_coordinator  = { units = 1 }
  loki_worker       = { backend_units = 1, read_units = 1, write_units = 1 }
  mimir_coordinator = { units = 1 }
  mimir_worker      = { backend_units = 1, read_units = 1, write_units = 1 }
  tempo_coordinator = { units = 1 }
  tempo_worker      = { compactor_units = 1, distributor_units = 1, ingester_units = 1, metrics_generator_units = 1, querier_units = 1, query_frontend_units = 1 }
  ssc               = { channel = "1/stable" }
  traefik           = { channel = "latest/edge" }
}

Apply complete! Resources: 87 added, 0 changed, 0 destroyed.

Upgrade Notes