Add securityContext to values.yaml and deployment templates

[fgeck]

Hello,

I would like to request the support for securityContext in the helm chart of portainer to be able to deploy the charts in a recommended secure way and avoid warnings like:

W0108 16:41:44.954400   40518 warnings.go:70] would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "portainer" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "portainer" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "portainer" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "portainer" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")