matrix: add fail2ban filter and jail
Test:
- On a production server apply the changes of MR !2296 (closed)
- Setup the fail2ban filter and jail, then restart fail2ban
- Trying to log in unsuccessfully from FluffyChat leads to a 10 min ban
In the previous commit the jail's name was above 29 chars which hindered iptables from effectively banning the Host IP, so I renamed it.
Signed-off-by: nbenedek contact@nbenedek.me