production/helm: Add emptyDir volume type to promtail PSP

[StevenReitsma]

What this PR does / why we need it:
Forgot that istio also needs emptyDir volume for #2355...

Which issue(s) this PR fixes:
Fixes #2355

Special notes for your reviewer:
Related PR: #2366

Checklist

• Documentation added N/A
• Tests updated N/A

[codecov-commenter]

Codecov Report

Merging #2379 into master will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2379      +/-   ##
==========================================
- Coverage   61.73%   61.66%   -0.08%     
==========================================
  Files         160      160              
  Lines       13569    13569              
==========================================
- Hits         8377     8367      -10     
- Misses       4565     4579      +14     
+ Partials      627      623       -4     

Impacted Files	Coverage Δ
pkg/promtail/positions/positions.go	47.32% <0.00%> (-13.40%)	⬇️
pkg/logql/evaluator.go	92.47% <0.00%> (-0.41%)	⬇️
pkg/promtail/targets/file/filetarget.go	70.48% <0.00%> (+1.80%)	⬆️
pkg/promtail/targets/file/tailer.go	78.40% <0.00%> (+4.54%)	⬆️

[cyriltovena]

LGTM