#155: Add correct pod security context values to pass kyverno tests for postgresql

General MR

Summary

This corrects the postgresql pod securitycontext configuration to pass kyverno tests, discovered during mergeback of the previous MR on #156 into the bigbang umbrella chart.

Relevant logs/screenshots

Before

0s (x17 over 6m2s)    Warning   FailedCreate            StatefulSet/mattermost-postgresql                       create Pod mattermost-postgresql-0 in StatefulSet mattermost-postgresql failed error: admission webhook "validate.kyverno.svc-fail" denied the request: 

resource Pod/mattermost/mattermost-postgresql-0 was blocked due to the following policies 

require-non-root-group:
  run-as-group: 'validation failure: validation error: runAsGroup must be set to an
    id > 0 in either spec.securityContext.runAsGroup or (spec.containers[*].securityContext.runAsGroup,
    spec.initContainers[*].securityContext.runAsGroup, and spec.ephemeralContainers[*].securityContext.runAsGroup).
    rule run-as-group[0] failed at path /securityContext/runAsGroup/'
restrict-host-path-write:
  require-readonly-hostpath: rule skipped

After, mattermost works and tests pass

Linked Issue

155

Upgrade Notices

N/A