Update peer strength metric computation to enable filtering by change author

[morucci]

Update peer strength metric computation to enable filtering by change author

Fixes: #1037

This change updates the computation where now we:

Find (and filter on) changes authors and for each of them find all event authors that did a comment/review on the change author.

The previous computation was that:

Find (and filter on) comments/reviews events authors and for each of them find all changes authors on which the event's author did a comment/review.

This change also:

• Updates the web UI for the peer strength to set the author colunm on the left.
• Keeps the previous computation code but unused for now. If the previous computation is relevant we could add a switch in the UI.