Track the TF spec migration for product modules

[MichaelThamm]

• Update the docs for TF usage and explanations: Tutorials, HowTo

For each charm repo (on main), we need to:

1. split the endpoints into requires/provides
2. create a designated TF tag so it can be sourced in the product modules.

For the stack we need to:

1. add variables for inputs: juju_controller, proxy, logging-config
2. add outputs: models, metadata

• optional: offers, credentials

Monolithics:

• alertmanager
  • fix: Split TF endpoints output to requires/provides alertmanager-k8s-operator#396
• catalogue
  • fix: Split TF endpoints output to requires/provides catalogue-k8s-operator#215
• grafana
  • fix: Split TF endpoints output to requires/provides grafana-k8s-operator#515
• loki
  • fix: Split TF endpoints output to requires/provides loki-k8s-operator#571
• prometheus
  • fix: Split TF endpoints output to requires/provides prometheus-k8s-operator#776
• opentelemetry-collector
  • fix: Split TF endpoints output to requires/provides opentelemetry-collector-k8s-operator#203

Microservices:

• loki
  • worker
    • fix: Split TF endpoints output to requires/provides loki-worker-k8s-operator#89
  • coordinator
    • fix: Split TF endpoints output to requires/provides loki-coordinator-k8s-operator#125
• mimir
  • worker
    • fix: Split TF endpoints output to requires/provides mimir-worker-k8s-operator#127
  • coordinator
    • fix: Split TF endpoints output to requires/provides mimir-coordinator-k8s-operator#211
• tempo
  • fix: Split TF endpoints output to requires/provides tempo-operators#274

Testing

1. Make sure to test the changes by running just terraform-validate in the observability-stack repo.
2. Update all READMEs for updates to the module sources, variable defaults, and outputs.