Allow injecting additional dashboards to DashboardCard with hook

[ivangonzalezacuna]

In some cases, somebody might need to generate extra dashboards (in our case, some default ones). We've been using this customization internally for some time and it works well.

To use it, just simply set the additionalDashboards that is now available in the EntityGrafanaDashboardsCard.

Also, I've exported the 2 types used in this plugin since they might be useful here.