Streaming support for attachments

[bschmalhofer]

Currently, when an user request to download an attachment the following happens:

• the webapp checks permissions
• it reads the complete file into process memory
• it generated a response containing the complete file

This means that large files eat up a lot of memory. A regular webserver does not do that when serving static files, the file is streamed. Gazelle does that too for the files in var/httpd/htdocs. See https://metacpan.org/pod/Plack::App::File. It would be nice if OTOBO could do that too. Of course this should also work for attachments served from S3.

[bschmalhofer]

Streaming has been implemented for article storage in S3. But IMHO nothing speaks against doing the same for file based attachments. I don't know whether it is possible for articles in the database backend.