Sort apt packages alphabetically within sections

[dguido]

Problem

The apt package list in the Dockerfile is not alphabetically sorted within each section, making it harder to spot duplicates and review diffs.

Current order:

fzf
ripgrep
fd-find
...
iptables
ipset
iproute2
dnsutils

Proposed fix

Sort alphabetically within each comment-delimited section:

fd-find
ripgrep
tmux
zsh
...
dnsutils
ipset
iptables
iproute2

Per @DarkaMaul's review feedback on trailofbits/skills#26.