Fix DNS config, expired certificates, and missing requirements

[Maspital]

This addresses a couple of small issues:

• The attacker did not have internet access post-provisioning due to missing DNS config
  • I opted to simply set it directly via /etc/resolv.conf, aka, without systemd-resolved
• The attacker couldn't access package repositories due to expired certificates
  • Fixed by adding the current keychain during the post-boot command
• The external mail handler running on the attacker is missing the aiosmtpd package
  • This change is recent, I simply forgot to also add this packet when updating from the deprecated smtpd
  • After fixing this, I've noticed that using input() within a service isn't a good idea, so I changed the service to simply run forever. It can still be restarted etc. with systemctl
• Sometimes, the Internet Router is unable to provide internet access to the rest of the network (and itself) for a short period of time
  • Bumping to the latest 2.x core version does not solve this
  • Seems to work reliably when explicitly setting DNS in /var/ipfire/dns/servers (I chose quad8)
  • On the same note, while upgrading from core141 to 157 on the internet router works without problems, it messes up the provisioning on the company router by preventing ansible from reconnecting after a restart (see here). We could still upgrade by running pakfire update/pakfire upgrade as the last provisioning step, but this takes quite a while, so I've opted to leave it at 141.

Resolves #93
Resolves #92
Also related to the mail handler issue mentioned in #80, but no longer relevant as the "buggy" part of the code has been replaced when switching to aiosmtpd

[Maspital]

Regarding upgrading IPFire on the Company Router:
If we want to do so in the future, remember that this also requires slight modifications to the boot command due to a layout change in IPFires menus (see commit).

[darshjain]

Hello, can you check up on this missing package as well

[ru37z]

Discussion required

[1ncludeSteven]

If you want to upgrade company router from IPFire2.25 to IPFire2.29, then current packetbeat version can not be executed correctly with error message runtime/cgo: pthread_create failed: Operation not permitted

[Maspital]

If you want to upgrade company router from IPFire2.25 to IPFire2.29, then current packetbeat version can not be executed correctly with error message runtime/cgo: pthread_create failed: Operation not permitted

We've decided to not upgrade the company router for now since the current older version works fine. But thank you for the heads-up!