www/nginx add a default value > 0 to ban_ttl to prevent UI slow down over time

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Is your feature request related to a problem? Please describe.

Our opnsense instances have gotten slower and slower over time, we even got connection aborts as soon, as we logged into web UI. I spent quite some time googling for solutions, but without finding related issues like #3397. Last week, the UI of one instance got unusable, so I investigated further. It turned out, that one PHP process, ngx_autoblock.php put 100% load on all CPUs by running multiple times. After analyzing the script, I found out, that the banned IPs are written to config.xml, on this instance 50k entries. By googling for a way to remove all entries, I found the issues, describing ban_ttl and the configuration field under advanced settings.

Describe the solution you'd like

I would add a default value other that 0 to the ban_ttl field, as 0 means to keep the IPs forever in the ban list. I have set my instances to 2880 (two days) this reduces the list to round about 100 entries. One of the issues mentions a value of 120 minutes which will aslo work - every value is better than indefinite.

Adding a value to the ban_ttl field will remove older IPs from the list as soon, as you press Apply - it takes some time but it works. (hint for People searching for slow OPNsense UI)

Describe alternatives you've considered

I have also considered the "Unlock All"-button in UI that is described in #4087 but it would require manual intervention.