:open_umbrella: Umbrella: migrate `Nina` to plugin system

[alessio-perugini]

Phase 1

• Write a proper Arduino Firmware Uploader plugin for Nina boards #188
• Add the usual number of workflows to the nina-fwuploader-plugin repo #191
• Add nina-fwuploader-plugin to the package-index.json #196
• Final testing of the Nina boards before releasing #193

Phase 2

• Migrate Nina firmwares to the new plugin system #195

Phase 3

• Clean up old Nina code as we're now using the plugin system #202
• Make a new release of arduino-fwuploader