Adding PreferAvoidPods annotation feature support in Poseidon/Firmament

[shivramsrivastava]

This PR adds the PreferAvoidPods annotation feature in Poseidon/Firmament. PreferAvoidPods annotation is used to avoid pods being scheduled to a specific node.

Any node with an annotation like below will not schedule those pods specified in this annotation by the Poseidon/Firmament scheduler on that node.

scheduler.alpha.kubernetes.io/preferAvoidPods

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shivramsrivastava

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes-sigs/poseidon/blob/master/OWNERS)~~ [shivramsrivastava] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[k8s-ci-robot]

Hi @shivramsrivastava. Thanks for your PR.

I'm waiting for a kubernetes-sigs or kubernetes 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.

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[deepak-vij]

/ok-to-test

[deepak-vij]

/lgtm

[deepak-vij]

/lgtm

[deepak-vij]

/ok-to-test