multithread: refactor multithread operation to use OpenChunkWriter if available #7056

If the feature OpenChunkWriter is not available, multithread tries to create an adapter from OpenWriterAt to OpenChunkWriter.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f