Migrate from dhcpcd to NetworkManager

[ethanjli]

This PR integrates PlanktoScope/pallet-standard#47 and PlanktoScope/pallet-standard#82 and thus fixes #250; this PR also adds some documentation to make progress on PlanktoScope/proposals#4. NetworkManager is used on both bullseye and bookworm. As part of this change, Forklift now must be run as the root user (i.e. sudo forklift), and Forklift's local data has been moved to the root user's home directory (i.e. /root).

TODOs:

• Check whether we still actually need to install hostapd
• Revert the switch to sudo forklift (including any changelog messages)
• Test the bullseye lite image on the RPi 4
• Fix issue with Docker & firewalld on bookworm
• Test the bookworm lite image on the RPi 4
• Test the bookworm lite image on the RPi 5
• Update device-portal infobox messages about planktoscope.local and pkscope.local
• Update setup & ops documentation about when planktoscope.local and pkscope.local work
• Update security-related ops documentation
• Add ops documentation about connecting a USB Wi-Fi dongle
• Add ops documentation about connecting to Wi-Fi networks (sudo nmtui to add the connection and then reboot)
• Add ops documentation about connecting to Wi-Fi networks with captive portals
• Update technical reference docs about system services and boot orderings
• Add technical reference docs about drop-in file fragment assembly system
• Add technical reference docs about firewalld
• Add technical reference docs about NetworkManager
• Add technical reference docs about machine-name generation and mDNS CNAME records (and why we have those aliases for the machine-specific hostname-based mDNS name)
• Add technical reference docs about pallet-standard's infra package deployments, including Docker networks, caddy-docker-proxy configuration, and prometheus configuration
• Update CHANGELOG.md

[ethanjli]

Note: the support that was added/integrated by this PR for a USB Wi-Fi dongle (including internet connection-sharing behavior through such a USB Wi-Fi dongle) has significant implications for #307 .