[FEAT] Add a plugin to translate/scroll the diagram with keyboard keys #167
Description
Describe the solution you'd like
Provide a KeysScrollPlugin that let scroll the diagram with the arrow keys of the keyboard.
The scroll will work when the focus is on the BPMN container.
This should work when the BPMN container has scrollbars
Additional context
In the future, we may let the user configure the keys (and even configure several keys to do the scroll).
We will probably use https://github.com/jgraph/mxgraph/blob/v4.2.2/javascript/src/js/handler/mxKeyHandler.js#L66
We may have to ensure there is a single instance of mxKeyHandler attached to the graph, so we may have to store a shared instance to ensure all plugins use the same instance.