[feature] Add reusable solution for turning choice fields into select2 autocomplete fields

[nemesifier]

We should look for a way to turn this into a reusable solution: openwisp/openwisp-firmware-upgrader#158.

It is possible that there are already some solutions out there, we should investigate.

[openwisp-companion]

This issue has been automatically assigned to @shivsubh who opened PR #642 to address it. 🎯