Add ability in a TestCase to manually inject beginning state data

### Use-cases

For some tests, its hard to get the TF state and upstream API in the proper state to reproduce observed issues (ie reading when deleting upstream without first creating then deleting through SDK, or some issues with provider upgrades or things that may not be possible in the API but possible in the UI, etc.). It may be useful (or in some cases just more expedient) to explicitly set the starting state for a resource in a `TestCase` prior to executing it.