feat(ws): add containerSecurityContext to WorkspaceKind

[thesuperzapper]

This PR brings the CRD spec into line with the latest updates from thesuperzapper/kubeflow-notebooks-v2-design@7aeb44d.

The most important changes are:

• Added a spec.podTemplate.containerSecurityContext to the WorkspaceKind
• Made all optional CRD fields into pointers
  • For example, we made WorkspacePodMetadata into *WorkspacePodMetadata
  • NOTE: this is required to distinguish between unset and empty values, and is recommended by Kubernetes.
• Updated the descriptions of CRD fields to keep them in line with the sample

[thesuperzapper]

@jiridanek @ederign @Adembc, for your reference.

[thesuperzapper]

@ederign while we wait for @jiridanek to be a member (so he can LGM), can you LGTM this so we can make future PRs based on it?

Since notebooks-v2 is not released its not a big deal if it's only a basic review.

[jiridanek]

/lgtm

[thesuperzapper]

@jiridanek thanks

/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jiridanek, thesuperzapper

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