Document Cosign steps in "Ratify on Azure"

[bspaans]

What would you like to be added?

The documentation for "Ratify on AWS" mentions a few steps to get cosign signatures working with Ratify, but this isn't mentioned on the "Ratify on Azure" page. This was a bit of a head-scratcher, because cosign can also use Azure Key Vault (AKV), but creates a Key, instead of a Cert, so ultimately doesn't work with Ratify.

Steps to get Cosign working on Azure:

• Setting cosign.key on the Helm chart
• Skip AKV setup
• Skip AKV config in Helm

Anything else you would like to add?

No response

Are you willing to submit PRs to contribute to this feature?

• [X] Yes, I am willing to implement it.