[feature] Add a dedicated page for showing devices on the map

[pandafy]

The goal is to add a dedicated view for viewing devices on the map. We have such a map on the dashboard, but it's size constraints (due to other UI elements) affects it's usability.

A dedicated page for using viewing all the devices on map would elevate such UX constraints.

This is a rough idea of what we want to achieve

[dee077]

Appraoch

• Add a new side menu link labeled Map using register_menu_group from opewisp-utils.
• Create a custom Django admin view to serve the dedicated map page, reusing the existing map template and configuration from the dashboard.
• Modify CSS to adjust the map height (currently limited to 300px).