[FEAT] Add a plugin to translate/scroll the diagram with keyboard keys

[tbouffard]

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.