Add an option to exclude anonymous users

[神代綺凛]

After #1264, I found my contributors image contain a lot of anonymous avatars.

I used to use some custom email addresses to commit in GitHub Actions. I don't need them to display in the image, because it will look ugly.

Could you consider adding this option?

Thanks for your work, this app is great!

[Suguru Inatomi]

@Tsuk1ko Thank you for the feedback! In a few weeks, I'll add an option like anon=1 to toggle the behavior.

[Suguru Inatomi]

@Tsuk1ko anon option is out! Including anonymous users is now an opt-in feature. They are not included by default.