#2308: Add extra few days in SuccessRateLine if survey is still running

[anaPerezGhiglia]

This is a follow up of #2336 suggestion comment

Also, @matiasgarciaisaia slack comment about the x-axis max value 👇

We're showing at least one month, but if the survey has been running for, say, 42 days - we show 42 days, then.
My suggestion was to add some extra days (say, 45, 47?) to give the idea of incompleteness.

Evidence

survey.state = running & started less than a month ago

survey.state = running & started more than one month ago

survey.state = terminated & started more than one month ago

for #2308

[matiasgarciaisaia]

👍