Update firewall and IP filtering UI labels and helper text

[buttondown-engineering]

@matt said:

1. instead of 'auditing mode,' just 'firewall', then 'Off/On'; with a separate control and explanation between 'Default/Aggressive' filtering
2. helper text should be clear 'The firewall will block subscribers we suspect are spam, bots, or other nefarious activity' with a link to more details about exactly what it entails
3. instead of 'enabled' / 'disabled' on 'handling blocked subscribers' (enabling what, exactly?), 'accept and mark as blocked', 'reject'
4. instead of 'IP address auditing', 'IP address filtering'
5. helper text should again say 'Buttondown will block subscribers with IP addresses we suspect are malicious.' With a callout to more info.
6. if enabled, check if the user is sending API activity, and if so, a big yellow banner 'ensure your API requests include IP addresses to avoid aggressive filtering' with a link to a help article

[linear-code]

BUG-401