v12 has removed the ModelConfig method. This is in preparation for 4.0
where we will change this facade to a multi-model facade. Calls to this
facade method were already removed in juju#17732.

v12 has removed the ModelConfig method. This is in preparation for 4.0
where we will change this facade to a multi-model facade. Calls to this
facade method were already removed in juju#17732.

v12 has removed the ModelConfig method. This is in preparation for 4.0
where we will change this facade to a multi-model facade. Calls to this
facade method were already removed in juju#17732.

#17761

v12 has removed the ModelConfig method. This is in preparation for 4.0 where we will change this facade to a multi-model facade. Calls to this facade method were already removed in #17732.

## Checklist

<!-- If an item is not applicable, use `~strikethrough~`. -->

- [x] Code style: imports ordered, good names, simple structure, etc
- [x] Comments saying why design decisions were made
- [x] Go unit tests, with comments saying what you're testing
- ~[ ] [Integration tests](https://github.com/juju/juju/tree/main/tests), with comments saying what you're testing~
- ~[ ] [doc.go](https://discourse.charmhub.io/t/readme-in-packages/451) added or updated in changed packages~

## QA steps

Bootstrap Juju, run `show-controller`, and check that the controller model version displays correctly:
```
$ juju show-controller | grep controller-model-version
 controller-model-version: 3.6-beta2.1
```

Run `upgrade-model` on the controller model, and check that it raises an error:
```
$ juju switch controller
$ juju upgrade-model
ERROR use upgrade-controller to upgrade the controller model
```

Run `destroy-controller` and check that the controller is successfully destroyed.

Bootstrap Juju again, and add the 3.6 controller to a 3.5 client:
```
juju3.6:~$ juju add-user juju35
User "juju35" added
Please send this command to juju35:
 juju register ...

juju3.6:~$ juju grant juju35 superuser
juju3.6:~$ juju grant juju35 admin controller
```
```
juju3.5:~$ juju register ...
```

Now do all the above steps again with the 3.5 client, to ensure compatibility between 3.5 and 3.6.

## Links

**Jira card:** JUJU-6351

- The `Controller` facade has become a multi-model facade.
- It now uses the following services: ModelService, ModelConfigService
  (for each model), AgentService
- Controller facade v11 has been removed, only v12 is supported in 4.0.
  The ModelConfig method no longer exists. All client methods are now
  using the ModelConfig facade instead (see juju#17732).
- Controller facade tests are slowly being ported over to using mocked
  services.
- The service factory now has methods `ModelAgent` which returns a
  model-scoped agent service, and `Agent` which returns a general agent
  service to access the agent version for any model. A
  `ControllerAgentVersion` method has been added for convenience.
- The ModelStatus api client decodes its errors using
  `params.TranslateWellKnownError`.
- Added a `CreateTestModelWithConfig` method to control parameters for
  created test models.

- The `Controller` facade has become a multi-model facade.
- It now uses the following services: ModelService, ModelConfigService
  (for each model), AgentService
- Controller facade v11 has been removed, only v12 is supported in 4.0.
  The ModelConfig method no longer exists. All client methods are now
  using the ModelConfig facade instead (see juju#17732).
- Controller facade tests are slowly being ported over to using mocked
  services.
- The service factory now has methods `ModelAgent` which returns a
  model-scoped agent service, and `Agent` which returns a general agent
  service to access the agent version for any model. A
  `ControllerAgentVersion` method has been added for convenience.
- The ModelStatus api client decodes its errors using
  `params.TranslateWellKnownError`.
- Added a `CreateTestModelWithConfig` method to control parameters for
  created test models.