[feature] Add popup on click of a node configurable from config

[dee077]

Feature Description

We need to add a pop-up on the click of a node, as here in the device-map.js in openwisp-monitoring layer.bindPopup can't be used, as we will be using echarts-leaflet to draw the nodes on the map. So we need our custom implementation of a similar functionality, which will be used on both the geo map and the floorplan map.

Approach

We can use the onClickElement event listener provided by the library to add the overlay and make it only work if it is set to true from the config.