Enable the helm chart users to customize the Security Context config.

[zamsong123]

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What would you like to be added:
Enable the helm chart users to customize the Security Context config.

Why is this needed:
For some of the enterprise users of the helm chart, there could be some security context check in the K8s clusters.
e.g. runAsNonRoot must be set to "true"
So it will be nice if we could enable the helm chart uses to config.

[zamsong123]

After analysis of the helm chart I notice there are 4 changes needed for this change:

1. daemonset under splunk-kubernetes-logging
2. daemonset under splunk-kubernetes-metrics
3. deploymentMetricsAggregator under splunk-kubernetes-metrics
4. deployment under splunk-kubernetes-objects

I will create a PR to make the change

[zamsong123]

Did some testing and below is the output:
splunk-connect-for-kubernetes % helm template . | grep securityContext -A10
securityContext:
allowPrivilegeEscalation: false
capabilities:
drop:
- ALL
readOnlyRootFilesystem: true
runAsGroup: 1001
runAsNonRoot: true
runAsUser: 1001
seccompProfile:
type: RuntimeDefault2222222

    securityContext:
      allowPrivilegeEscalation: false
      capabilities:
        drop:
        - ALL
      readOnlyRootFilesystem: true
      runAsGroup: 1001
      runAsNonRoot: true
      runAsUser: 1001
      seccompProfile:
        type: RuntimeDefault44444

--
securityContext:
allowPrivilegeEscalation: false
capabilities:
drop:
- ALL
readOnlyRootFilesystem: true
runAsGroup: 1001
runAsNonRoot: true
runAsUser: 1001
seccompProfile:
type: RuntimeDefault333333

    securityContext:
      allowPrivilegeEscalation: false
      capabilities:
        drop:
        - ALL
      readOnlyRootFilesystem: true
      runAsGroup: 1001
      runAsNonRoot: true
      runAsUser: 1001
      seccompProfile:
        type: RuntimeDefault1111111