Duration limit customisation

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

I'm confused when I see long duration in stats and it just gone.

**💡 Describe the solution you'd like**

I would like to have an option to set another duration limit. After code analysis, I know the limit is 30 minutes.

The perfect solution would have dedicated section in Settings panel, between Events and Permanent Tokens sections.
The section should have nice UI, including:

- integer value range input from 1 to 60
- switch/select for unit - minutes or hours

As far I noticed, the change will have an impact in API resolvers:

- Facts.activeVisitors
- DomainStatistics.durations

**❓ Describe alternatives you've considered**

Minimal solution could be by adding environment variable.
But I'm not a big fun of this approach as it's not intuitive and needs documentation reading.

**📋 Additional context**

In my case, I have tutorial like contents on my pages so the reader could need more time to spend at my pages than half an hour.
This caused by they need to read an article first, understand it and try to apply the solution to own project.
It's time consuming and I feel 30 minutes is too short for this scenario.

I need to change it, perhaps a few times, and figure out the best duration limit for me.
I can involve to implement this feature :)