[Doc] Document how Ratify supports cert day 2 operation including Cert revocation/rotation/expiry

[susanshi]

What would you like to be added?

During a community meeting, we agreed to add more docs for the current supported scenarios around Cert revocation/rotation/expiry.

Anything else you would like to add?

No response

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

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

[susanshi]

Discussed in community meeting, this is to track if Ratify should have customer guide on how to handle cert revokation/rotation/expiry scenarios after time stamping support.