[Small Feature] Configurable Temp Directory to fix RAM bloat

[Arcitec]

Motivation
It currently uses os.tmpdir() (which is /tmp) to write all the output. This is a problem because that's a tmpfs by default, meaning that it's RAM-backed storage which wastes system RAM as ChaiNNer fills it with processed temp-images:

tmpfs on /tmp type tmpfs (rw,nosuid,nodev,seclabel,size=32767284k,nr_inodes=1048576,inode64)

It's also a privacy problem, because as the tmpfs fills up, it can page to swap.

Description

A new option in the settings:

• ChaiNNer -> Settings -> Environment -> Temp Directory:
  • System Default: /tmp (show os.tmpdir() value here)
  • Custom Location: (...)

Alternatives
There doesn't seem to be any solutions at the moment.