Add config to save stereoscope / vulnerability scans to a custom folder intead of /tmp

[crlsgms]

Is your feature request related to a problem? Please describe. Yes, enabling the vulnerability scans get piling up my /tmp folder very quick, that lots of data is downloaded, ad screenshots I need it to be configurable or someway to move it elsewhere.

Describe the solution you'd like on k9s info there is nothing about the stereoscope-xxx files, also not mentioned on the config parameters

Describe alternatives you've considered maybe have a new env var or config entry will do

Additional context example of the size that quick got used on my /tmp folder:

┌─[root]@[cgomes2]:/tmp
└──> # du -h -d 1 stereos*
4.0K    stereoscope-2584689121/docker-daemon-image-2051082326
8.0K    stereoscope-2584689121
4.0K    stereoscope-2761211374/docker-daemon-image-1170164696
8.0K    stereoscope-2761211374
165M    stereoscope-3042448445/docker-tarball-image-1622628918
165M    stereoscope-3042448445/docker-daemon-image-1323028352
330M    stereoscope-3042448445
4.0K    stereoscope-4172588425/docker-daemon-image-1327426436
8.0K    stereoscope-4172588425
┌─[root]@[cgomes2]:/tmp
└──> # ls -lha stereos*
stereoscope-2584689121:
total 20K
drwx------  3 root root 4.0K Sep  4 05:27 .
drwxrwxrwt 20 root root  12K Sep  4 05:28 ..
drwx------  2 root root 4.0K Sep  4 05:27 docker-daemon-image-2051082326

stereoscope-2761211374:
total 20K
drwx------  3 root root 4.0K Sep  4 05:27 .
drwxrwxrwt 20 root root  12K Sep  4 05:28 ..
drwx------  2 root root 4.0K Sep  4 05:27 docker-daemon-image-1170164696

stereoscope-3042448445:
total 24K
drwx------  4 root root 4.0K Sep  4 05:27 .
drwxrwxrwt 20 root root  12K Sep  4 05:28 ..
drwx------  2 root root 4.0K Sep  4 05:27 docker-daemon-image-1323028352
drwx------  2 root root 4.0K Sep  4 05:27 docker-tarball-image-1622628918

stereoscope-4172588425:
total 20K
drwx------  3 root root 4.0K Sep  4 05:27 .
drwxrwxrwt 20 root root  12K Sep  4 05:28 ..
drwx------  2 root root 4.0K Sep  4 05:27 docker-daemon-image-1327426436```