Issue 623: add security context override to operator deployment (#623)

[Hexoplon]

Change log description

• Add podSecurityContext and securityContext overrides to Zookeeper Operator deployment in helm chart
• Updated README for helm chart

Purpose of the change

Fixes #623

What the code does

Updated the Zookeper Operator helm chart to include the already existing securityContext section in the helm chart values.yaml file. Now, the securityContext values are correctly added to the operator Deployment. This ensures that the operator can run in a Kubernetes cluster where Pod Security Admission is enforced, and running in restricted mode.

How to verify it

Add custom settings to securityContext and/or podSecurityContext, and verify that the deployment object has been updated using: kubectl -n <namespace> describe deployment zookeeper-operator

[Saremox]

We're making usage of pod-security.kubernetes.io/enforce = restricted in all our clusters as a hardening measure. Would love to see this PR in the next version.