The possibility to add and edit icons should be added to the rich text bar in Knowledge Base. It is a very handy and a really nessicary feature to add icons in help articles. This can be used to indicate buttons, improve readability, etc. This feature is already available in other parts of HubSpot and other Help Site solutions have this feature. Below is an example from Canva's help site, where they use icons.
It is a simple thing but it improves the overall look of a help site a lot and makes explaining different things a lot easier.