API v4 collections controller, serializer and routes

[louispt1]

Context

Split out of the old api-v2 branch. This branch and api-v4-saved-scenarios both add the v2 namespace to routes.

Decisions

• This is built based on Collections relying on SavedScenarios, so it cannot be merged until the Collections model has been migrated to rely on SavedScenarios.
• Membership is scoped based on what the collection's owner can see based on SavedScenarioUser
• There was a bug with the version_consistency method relying on .map which has been resolved so errors can see what's happening via filter_map.
• shared_access on CollectionSavedScenario called saved_scenario.viewer? without checking the association resolved which would have raised an error

Implemented changes

• /api/v2/collections for index, show, create, update, destroy, discard and restore.
• CollectionSerialiser contains an allow-list, so new database columns have to join the public API contract explicitly

Related

Goes with #295