Cleanup GitHub org file

[thesuperzapper]

This PR does NOT add or remove any members from teams, it is only about cleaning up the org.yaml file.

Actions Taken:

1. Use members rather than maintainers to define teams
   • Without this change, non-org-admins can make additions/removals to teams without making PRs into this repo
   • This is recommended at the top of the org.yaml file.
2. Sorts all members and repos lists alphabetically
3. Removes references to repos that were deleted in Archive inactive Kubeflow repos community#479:
   • kubeflow/fastpages
   • kubeflow/features
   • kubeflow/homebrew-cask
   • kubeflow/homebrew-core
   • kubeflow/triage-issues
4. Sets the description of company teams as:
   • Team of members from {COMPANY_NAME}
5. Sets the description of teams that give write access to a single repo as:
   • Maintainers of {REPO_NAME}
6. Sets the description of Working Group teams as:
   • Team of {GROUP_NAME} Working Group leads

[thesuperzapper]

/assign @zijianjoy

[thesuperzapper]

@zijianjoy I have rebased this PR, I would appreciate your approval as soon as you can.

This PR is important because it:

1. Close a security hole (stop defining GitHub team members as managers, as this allows adding/removing members outside of this PR process, potentially resulting in privilege escalation)
2. Cleanup the names of the GitHub teams
3. Remove references to deleted GitHub repos

[zijianjoy]

/lgtm
/approve

Thank you Mathew for keeping the org file up-to-date and following standard!

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: thesuperzapper, zijianjoy

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