First draft of moving API server TLS cert generation to controllers

- Refactors the existing cert generation code into controllers
  which read and write a Secret containing the certs
- Does not add any new functionality yet, e.g. no new handling
  for cert expiration, and no leader election to allow for
  multiple servers running simultaneously
- This commit also doesn't add new tests for the cert generation
  code, but it should be more unit testable now as controllers

README.md

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-# placeholder-name
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+Copyright 2020 VMware, Inc.