Fix default grouping step for new line chart

[acelaya]

Shlink web client version

• Version: 2.5.0
• How do you use shlink-web-client: All

Summary

Shlink v2.5.0 introduces a new line chart where you can see how many visits a link received during time.

It allows to show visits per hour, day, week and month, being the last one the default value.

However, that makes no sense for too young short URLs, as it only shows one dot for a long time.

Change the default value to be dynamic, following this logic:

• Default to hourly when the short URL is younger than 2 days.
• Default to daily when the short URL is between 2 days and 1 month old.
• Default to weekly when the short URL is between 1 and 6 months.
• Default to monthly for short URLs older than 6 months.

The reference date should be the one in which the first visit occured.