[elasticsearch] Add securityContext to keystore container

[ebuildy]

Describe the feature:

Currently, only main container have a securityContext configurable via values.yaml (https://github.com/elastic/helm-charts/blob/master/elasticsearch/templates/statefulset.yaml#L223), in order to improve security, initContainer keystore (https://github.com/elastic/helm-charts/blob/master/elasticsearch/templates/statefulset.yaml#L173) should have it too.

Describe a specific use case for the feature:

This is a good thing to match k8S best-practices, especially when using Fairwinds Polaris.

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[botelastic]

This issue has been automatically closed because it has not had recent activity since being marked as stale.