Add ability to delete a correlation context

[bvandewe]

What would you like to be added:

The ability to delete an existing context in a correlation.

The API currently enables to DELETE a correlation altogether, but not its context(s). (thought there's an issue with the DELETE, separate ticket).

Why is this needed:

At this point, i'm not 100% sure how this happened, but a correlation context was not deleted automatically as expected and can hardly find the server logs

This is low priority as far as im concerned.