OpenStack Swift (and others) Streaming support

[llebout]

Note: I have OpenStack Swift as Primary Storage

Is your feature request related to a problem? Please describe.
It causes a misunderstanding to users when they are waiting for the server to download files from object storage to then only start the download in their web browser

Describe the solution you'd like
It would be better if Nextcloud could start downloading the object from the object storage store at the same time as it offers the download to the user (streaming the data through)

[adrb]

Fixed in pull request #18883

[llebout]

@adrb Super cool! Thanks a lot.