Making repo method behavior more consistent

[talanknight]

This PR makes several changes to make the interface w/ the repos consistent.

1. ListTargets now behaves like other ListX resources, taking in a slice of scopes.
2. Decrease the number of checks done when creating an in memory resources, instead relying on the methods which persist them in the DB to check that specific fields are set
3. Deleting most resources from a db requires a scope to be passed in. This scope value isn't verified in the repo in any way but is used, in most cases, for oplog generation.

This work makes the repos more uniform which would make generating handler code easier if we decide to go that route in the future, or when creating libraries or applying new requirements.

Future work will include requirements around scope id being present in oplogs, update mask related code generation.

[hashicorp-cla]

All committers have signed the CLA.