Use `committed_date` instead of `authored_date` when showing a commit

What does this MR do?

Before, we showed the committed_date of commits in commits list, but the authored_date in the commit. This could be confusing as for both we prefix the date by Authored by.

Unless you guys have an opinion about this and intentionally show committed or authored dates depending on the view, I think this might be confusing and I think the committed_date should be the prevalent. Authored date could be also shown in the commit show view as an additional detail. first.

In the same vein, I'd suggest to group commits in commits list by authored date and not committed date, but this could be discussed in a separate issue.

NB: In the wiki related views, we show authored_date and it makes more sense as we want to show the last updated date.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together