Update the Scenario behaviour when using action params not defined in the schema

[tonyandrewmeyer]

We should make sure that Scenario properly reflects the additionalProperties field in actions.yaml or charmcraft.yaml. The consistency checker should error if additional properties are not allowed and the event provides one that isn't defined in the schema.

Note that Juju 4 reverses the default value so we need to handle that based on the mocked Juju version.

This should help people identify that they need to explicitly set additionalProperties=true for Juju 4, if their integration tests aren't covering this behaviour.