chore(trainer): Add architecture section and diagram to Execute TrainJobs Locally section

[Fiona-Waters]

Description

Following on from https://github.com/kubeflow/website/pull/4221 and based on this comment we should create and add an architecture section and diagram to local_process.md. The same could be done for docker.md and podman.md

Component/Kubeflow Version:

Labels

/area trainer

/area website

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