Add option to configure pod and container level securityContext

**Is your feature request related to a problem? Please describe.**
It's becoming more common to restrict application namespaces with Pod Security Admission (https://kubernetes.io/docs/concepts/security/pod-security-admission/) especially with restricted Pod Security Standard (https://kubernetes.io/docs/concepts/security/pod-security-standards/#restricted).
Unfortunately currently there is no flexible option to configure `securityContext` for pods and containers (e.g. vault-agent-injector) via helm values.

**Describe the solution you'd like**
Add option to configure pod and container level `securityContext` via helm values. In order to be compliant with restricted Pod Security Standard, container's `securityContext` would need to look similar to:
```
securityContext:
allowPrivilegeEscalation: false
capabilities:
drop:
- ALL
runAsNonRoot: true
seccompProfile:
type: RuntimeDefault
```

Start by locating the Helm values and templates that render pod and container settings, including the vault-agent-injector resources. Compare the rendered manifests with the restricted Pod Security Standard requirements and use Helm rendering to verify the values. Done means both pod-level and container-level securityContext can be configured through Helm values.

Written by the indexing model from the issue text.