Lead Verifier Documentation

[yogeshbdeshpande]

This is a top level issue that tracks introduction of New Documentation for Veraison due to addition of a Lead Verifier Feature:

Especially:

Documentation changes required in:

1. https://github.com/veraison/docs/blob/main/api/well-known/README.md Here the Composite Media Types needs to be Introduced.
2. The Veraison Book needs to change.
3. A description of new schemes in Verification documentation needs to change
4. Any further items will be listed here..