Include kubectl command metadata in http request headers

[pwittrock]

Enhancement Description

• One-line enhancement description (can be used as a release note): kubectl adds http headers with the subcommand name, which flags were specified and a session id.
• Kubernetes Enhancement Proposal: https://github.com/kubernetes/enhancements/tree/master/keps/sig-cli/859-kubectl-headers
• Discussion Link: https://groups.google.com/g/kubernetes-dev/c/y4Q20V3dyOk/m/ozSUR3dJDQAJ
• Primary contact (assignee): @soltysh @pwittrock
• PRs by stage and milestone:
  • Alpha - v1.21
  • Beta - v1.22
  • Stable - v1.35
    • KEP (k/enhancements) update PR(s):
      • KEP-859: promote command headers to stable #5637
    • Code (k/k) update PR(s):
      • Promote KUBECTL_COMMAND_HEADERS to stable kubernetes#134777
    • Docs (k/website) update PR(s):
      • Remove KUBECTL_COMMAND_HEADERS which is promoted to stable website#52871

[pwittrock]

cc @kubernetes/sig-api-machinery-misc
cc @kubernetes/sig-cli-misc
cc @soltysh
cc @deads2k

[kacole2]

@pwittrock can you please update the original post with the correct formatting so we have consistency?

# Enhancement Description
- One-line enhancement description (can be used as a release note):
- Kubernetes Enhancement Proposal: (link to kubernetes/enhancements file, if none yet, link to PR)
- Primary contact (assignee):
- Responsible SIGs:
- Enhancement target (which target equals to which milestone):
  - Alpha release target (x.y)
  - Beta release target (x.y)
  - Stable release target (x.y)