Add fail2ban configuration guide

[UnicodeApocalypse]

Hello,

I just made a small guide to help users configure fail2ban with Komga. Informations can be found on internet but I think it deserves to be in official guides

[gotson]

i don't use fail2ban, but this is probably not the best way to configure it. Komga runs with Spring Boot, which uses Apache Tomcat, which can be configured to generate standard access.log, which i suppose fail2ban would most likely support natively, or at least with wide community support.