[feature] Frontend - Location Selection in Mass Upgrade UI

[youhaveme9]

Title

Add Location Selection UI for Mass Firmware Upgrades

Context / Approach

To support location-based mass firmware upgrades, we need to update the admin interface to allow selecting locations when initiating a mass upgrade.

My approach will be to:

1. Add a location autocomplete field in the mass upgrade confirmation form
2. Add a location filter in the BatchUpgradeOperation admin list view
3. Update admin templates to display location information in the upgrade confirmation and detail views
4. Update API endpoints to support location-based filtering
5. Update the README documentation to include information about location-based upgrades

This UI implementation will follow OpenWISP's design patterns, using autocomplete fields for better performance with large datasets and maintaining consistency with the existing group selection interface.

Dependencies

• Depends on the backend implementation of location-based mass firmware upgrades
• Requires the admin UI changes for group-based upgrades to be completed first