Set all translation authors and commit authors

[bugzilla-to-github]

This issue was created automatically by a script.

Bug 1522112

Bug Reporter: @mathjazz
See also: https://bugzilla.mozilla.org/show_bug.cgi?id=1521288

Ideally, Pontoon should split commits containing translations from multiple authors into multiple commits, one for each author.

Such change would require a pretty serious refactoring of our sync code, so we should start with a simpler, short-term solution.

Instead of setting one user (the one with most contributions) as the commit author, we should set all contributors as authors.

[eemeli]

During the discussions around #3312, we determined not to do this.