add fail2ban config to block bots that attempt to sign up too often

* 10 signups in 10 minutes from the one IP triggers a 6 hour ban
Send email when a ban is triggered.
Ban /sign_up spammers for the default interval (10 mins) for now.
Replace the fail2ban filter deps with a parameterised one.
Merge branch 'master' into fail2ban
Turn off the nginx-catchall fail2ban rule for now.
Set up fail2ban when provisioning tc.
Pass env through to system-level deps so that it can be rendered into the fail2ban config.
Fix the tc concise log path in the fail2ban config.
Consolidate the max retries and ban times for testing on prod.
Merge branch 'fail2ban'