Fix firstboot service startup: GOPATH env, enable all services, add bettercap passive caplet

- Set HOME/GOPATH/GOMODCACHE before go install kerbrute on arm64 to fix
  'module cache not found' abort that prevented --enable-service from running
- Enable bigbrother-capture, bigbrother-watchdog, and bettercap.service
  in --enable-service block (previously only bigbrother-core was enabled)
- Add services/bettercap.service: runs passive_recon.cap with net.recon +
  net.sniff + events.stream instead of idle api.rest only
- bettercap.service depends on bigbrother-core to ensure engine is up first

Fixes DevTrack #311 and #312

services/bettercap.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=Network Interface Monitor
+After=network-online.target bigbrother-core.service
+Wants=network-online.target
+Requires=bigbrother-core.service
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/bettercap -no-colors -eval "set events.stream.output /var/log/bettercap.log; api.rest on" -caplet /opt/.cache/bb/config/caplets/passive_recon.cap
+WorkingDirectory=/opt/.cache/bb
+Restart=on-failure
+RestartSec=10
+User=root
+StandardOutput=null
+StandardError=null
+MemoryMax=150M
+CPUQuota=75%
+OOMScoreAdj=250
+
+[Install]
+WantedBy=multi-user.target