Add "abuse functionality" to Impactful functionality

[sanAnand]

While Unauthorized Data Access and State-Changing Actions cover most of the impact of Prompt Injection attacks, there are two other, non-overlapping impacts:

1. Money loss. As mentioned later in the post, cost overruns are a legitimate concern and prompt injection can be used to affect that.
2. DoS: If rate-limiting is in place as a control, the control can be exploited through prompt injection to cause a denial of service.

To cover the above risks, you should consider adding a broader "abuse of functionality" (or similar) category.