[Feature] Add AllowPrivilegeEscalation to container's securityContext

[captnbp]

PR summary

KubeSpawner can spawn pods and container's with a securityContext field set.

The notebook container can only be set with the following security features:

• run_as_uid
• run_as_gid
• fs_gid
• supplemental_gids
• run_privileged

But in some restrained security context, we need to disable privilege escalation for the notebook container.
By default, AllowPrivilegeEscalation is kept as True. We need a way to set it to False if needed.

Proposed change

Add allow_privilege_escalation flag to be able to set it to False.

The target flags will be:

• run_as_uid
• run_as_gid
• fs_gid
• supplemental_gids
• run_privileged
• allow_privilege_escalation

Who would use this feature?

People with restrained security context, even for notebook container.

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[captnbp]

Will fix failing checks tomorrow.

[yuvipanda]

Thank you very much for the PR, @captnbp! I do this all the time to my own deployments, very highly recommended.

Will happily merge this once the tests are fixed.

[captnbp]

@yuvipanda all checks passed ! :-)

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[consideRatio]

Thank you @captnbp! 🎉 ❤️ 🌻 !!