Centralize all purge API calls

api/custom/purge.go

database/table_media.go

database/table_reserved_media.go

database/table_thumbnails.go

migrations/23_add_datastore_locations_indexes_down.sql

migrations/23_add_datastore_locations_indexes_up.sql

pipelines/_steps/upload/generate_media_id.go

tasks/task_runner/purge.go

tasks/task_runner/purge_remote_media.go