KEP-2170: Add manifest overlays for standalone installation

[Doris-xm]

What you would like to be added?

Add support for a standalone installation where the manager and runtimes are included together. This would simplify the installation process.

cc @kubeflow/wg-manifests-leads @kubeflow/wg-training-leads @andreyvelich @Electronic-Waste

Why is this needed?

As discussed in #2382, we can use fifo sortOption to provide a streamlined setup process, eliminating the need for separate overlays.

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[Doris-xm]

/assign

[Electronic-Waste]

/remove-label lifecycle/needs-triage
/release 2.0

[juliusvonkohout]

I just noticed that the base https://github.com/kubeflow/trainer/blob/0a498fef86bc1417bdff0d2f6c17bffa2e90777e/manifests/base/manager/manager.yaml is missing the securitycontext. See kubeflow/katib#2528 as reference. Please add a securitycontext that satisfies PSS restricted https://kubernetes.io/docs/concepts/security/pod-security-standards/ to all of the pods you create.