Potential SELECT/INSERT Race Condition in Batch Creation API

[jkva]

As demonstrated by the ActiveRecord::RecordNotUnique exception raised within Api::ResourcesController#create_many - https://sentry.io/organizations/coyote-org/issues/3016859111/

This likely happens because of the underlying Resource::find_or_initialize_by_canonical_id_or_source_uri - initlalisation doesn't create a record, the record is created by another parallel process, and when this Resource is saved, a RecordNotUnique exception is thrown via Postgres.

This code should be modified to use optimistic insertion by use of create_or_find_by.