Show average instead of median as it's a more reliable metric for know how long PRs takes

[eduardoacskimlinks]

Although it's a valid way of understanding the time it takes to review a pull request, in many cases, we want to show the average time it takes for some people to review a pull request because we aim to improve productivity or highlight an issue within our review process.

Therefore, how hard will it be to provide a new parameter to select what time scale we want to use to calculate the time column?

For example, in the images below, we can see when the median doesn't show the reality of the review speed.

[eduardoacskimlinks]

This is a draft of the concept. I can convert it into an actual pull request if this is something that will be considered to be merged #81