Create tooling to generate / manage KEPs

Create tooling to:
- generate KEP directories and associated metadata
- graduate KEPs through approval phases
- convert existing KEPs from flat-files to directory structure (https://github.com/kubernetes/community/issues/2725)

Work item for https://github.com/kubernetes/features/issues/617

/kind feature
/sig pm
/milestone v1.13
/assign @calebamiles 