Move pipelines around a bit

api/r0/download.go

api/r0/upload.go

api/v1/create.go

pipelines/_steps/download/open_stream.go

pipelines/_steps/download/try_download.go

pipelines/_steps/quota/check.go

pipelines/_steps/upload/blurhash_async.go

pipelines/_steps/upload/deduplicate.go

pipelines/_steps/upload/generate_media_id.go

pipelines/_steps/upload/limit.go

pipelines/_steps/upload/lock.go

pipelines/_steps/upload/quarantine.go

pipelines/_steps/upload/redis_async.go

pipelines/pipeline_create/pipeline.go

pipelines/pipeline_download/pipeline.go

pipelines/pipeline_upload/pipeline.go