Request: run your own Sigstore documentation

[znewman01]

The beginnings of this exist already:

• https://docs.sigstore.dev/cosign/custom_components
• #19

But I propose the following reorganization:

• Run your own Sigstore
  • Overview
  • Scaffolding
  • Managing keys with TUF (this would mostly pull from "Configuring Cosign with Custom Components")
    • TUF
    • Revocations (#19)

This should eliminate most of "Configuring Cosign with Custom Components," so we could drop that page and make it an FAQ.