feat(backend + SDK): Add backend and SDK support to use Kubernetes FieldPath as env

[Tomcli]

Description of your changes:
fixes #10155
Add backend and SDK support to use Kubernetes FieldPath as env. This follows the Kubernetes document is set field as env variables. https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/

This feature enables users to get information about the running pod such as metadata labels/annotations without gaining extra permission.

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[Tomcli]

/assign @connor-mccarthy
/assign @chensun

[chensun]

/lgtm
/approve

Thanks!

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chensun

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Needs approval from an approver in each of these files:

• backend/OWNERS [chensun]
• kubernetes_platform/OWNERS [chensun]

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[Tomcli]

Thanks @chensun, I fixed the PR conflicts and it's good to go now.

[rimolive]

/retest

[Tomcli]

Hi @rimolive, could you help review this PR and leave a lgtm. I have rebased this PR and is good to go, just need someone to double check and lgtm.

[rimolive]

/lgtm

[google-oss-prow]

@Tomcli: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
kubeflow-pipelines-samples-v2	489ce7f	link	false	/test kubeflow-pipelines-samples-v2
kfp-kubernetes-execution-tests	489ce7f	link	false	/test kfp-kubernetes-execution-tests

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