Add security context to the chart

[nabokihms]

https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-the-security-context-for-a-pod https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-the-security-context-for-a-container

Closes https://github.com/deckhouse/k8s-image-availability-exporter/issues/56

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1154aff) 20.00% compared to head (ec448a0) 20.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #94 +/- ## ======================================= Coverage 20.00% 20.00% ======================================= Files 4 4 Lines 570 570 ======================================= Hits 114 114 Misses 448 448 Partials 8 8 ```

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