Add support for dbpurgeage (required for recidive)

[john-999]

The Role should ideally accept the below configuration's last line (but it does not set the value):

- name: "Install : fail2ban."
  include_role:
    name: oefenweb.fail2ban
  vars:
    fail2ban_dbpurgeage: 648000 # For use of the jail "[recidive]": Increase this value to e.g. 648000 (7.5 days)

Extract from the fail2ban docs (https://wiki.meurisse.org/wiki/Fail2Ban#Recidive) regarding the [recidive] jail:

# 2. If you increase bantime, you must increase value of dbpurgeage
#    to maintain entries for failed logins for sufficient amount of time.
#    The default is defined in fail2ban.conf and you can override it in fail2ban.local

[tersmitten]

Can you make a pull request?