Adding "is not related to" operator to relational field condition rules

[adrianjean]

Currently, relational field conditions for Categories, Tags, etc. only support:

Is related to
Has value
Is empty

I would like to add a fourth operator — is not related to — that excludes entries related to specific elements.

I used AI to create a patch (attached) to add this and I tested it against CraftCMS 5.10.5 and it's working. The patch applies changes to RelationalFieldConditionRule. Sharing here in case it's helpful!

Patch:
relational-field-not-related-to.patch