[stable/prometheus] Disable "enableServiceLinks" on Kubernetes prior 1.13

[atkrad]

What this PR does / why we need it:

I use K8s prior 1.13 when I've applied the Prometheus statefulset this error occurred:
Error: unable to build kubernetes objects from release manifest: error validating "": error validating data: ValidationError(StatefulSet.spec.template.spec): unknown field "enableServiceLinks" in io.k8s.api.core.v1.PodSpec
because the field doesn't available for prior version 1.13

Which issue this PR fixes

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [stable/mychartname])

[k8s-ci-robot]

Hi @atkrad. Thanks for your PR.

I'm waiting for a helm member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[zanhsieh]

/assign
/ok-to-test

[zanhsieh]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: atkrad, zanhsieh

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