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. Tagging for TF modules in charm repos observability#427
3. add a providers.tf and terraform.tf file, where the terraform.tf file basically becomes what was our providers.tf and the providers.tf becomes the implementation (with config) for the Juju provider.
4. Add a description to the constraints Terraform input variables so people know that this applies to all workload containers.
   5. Make sure this is clear in the TF provider docs for that variable since the stack blindly points at it per charm variables.
   6. k8s resource patch is losing the fight with juju observability-libs#128

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

Mesh charms:

• @adhityaravi

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.