Add lifecycle key to integrations

[Abuelodelanada]

@amandahla mentioned:

For all juju_integration: Is there any situation where source/target application could be re-deployed?

If yes, then a lifecycle might be needed like the one in the documentation:
https://registry.terraform.io/providers/juju/juju/latest/docs/resources/integration

@Abuelodelanada said:

Oh, the lifecycle key is interesting!

I think it depends on the scope of this cos module. For a first version I would think we don't need it.

WDYT @sed-i ?

@MichaelThamm said:

I think this comment from @amandahla is important. This lifecycle option in the juju_integration was added due to this issue:

• Replaced units lose relations juju/terraform-provider-juju#401

Which includes these steps to reproduce:

1. Deploy an application with relations via terraform.
2. Change its constraints and terraform apply
3. See the relations are lost, rerun terraform apply to restore relations.

Our modules support constraints and there may be other scenarios (none that I know of) where TF may remove an application and then the relation is missing unless someone manually runs terraform apply.

This would affect the robustness of our TF deployment if not implemented, although a rare scenario.

[sed-i]

We should try to understand:

• Is the lifecycle an important concept in the juju-tf "state model" or if it's just a temporary workaround.
• What would be the implications on our models. If it's minor then might as well just do it.