KEP 5075: update API description, add alternatives, update test plan

[sunya-ch]

• One-line PR description: Update API descriptions, add alternatives and test plan those have been discussed and suggested after the previous PR merged.

• Issue link: DRA: Consumable Capacity #5075

• Other comments:

  The changes are related to suggestions from @pohly @LionelJouin @mortent @liggitt @lmktfy.

  What not included yet are:

  • Discussion about claimTracker

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @sunya-ch. Thanks for your PR.

I'm waiting for a 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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