Set security context for polaris

[mlevesquedion]

This PR adds SecurityContexts to the polaris Job in order to run the job with the least amount of privilege possible, in partial fulfillment of #163.

I ran the job with and without the changes in a local kind cluster and I did not see a difference in the output.

To obtain the output, I ran:

kubectl create deployment nginx --image nginx:1.16
kubectl wait --for=condition=available deploy/nginx --timeout=60s
./bin/starboard scan configauditreports deployment/nginx
./bin/starboard get configaudit deployment/nginx -o yaml >cars.yaml

[codecov]

Codecov Report

Merging #360 (5f23290) into main (ab281e4) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #360      +/-   ##
==========================================
+ Coverage   66.35%   66.52%   +0.16%     
==========================================
  Files          58       58              
  Lines        3026     3041      +15     
==========================================
+ Hits         2008     2023      +15     
  Misses        769      769              
  Partials      249      249              

Impacted Files	Coverage Δ
pkg/polaris/plugin.go	91.17% <100.00%> (+1.09%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ab281e4...5f23290. Read the comment docs.

[danielpacak]

LGTM! Thank you @mlevesquedion !