[FEATURE] Ability to set isPermaLink="false" for guid

[AyumuKasuga]

Is there an existing feature request for this?

• I have searched the existing feature requests

Is your feature request related to a problem? Please describe.

Currently, if we use not a real URL for <guid> in RSS, we get this message from validation tool: https://validator.w3.org/feed/docs/error/InvalidHttpGUID.html

Describe the solution that you would like.

As I understand we can use a special type for Item.Id (as we use for Link for example), ans allow user to set isPermaLink value. What do you think?

Describe alternatives you have considered.

No response

Anything else?

No response