Matomo core developers  are recommended to use "js/" instead of "piwik.js" and "piwik.php":
- js/index.php (or implicitly as "js/") can be used to serve up the minified piwik.js;
- it supports conditional-GET and Last-Modified, so piwik.js can be cached by the browser;
- it supports deflate/gzip compression if your web server (e.g., Apache without mod_deflate or mod_gzip), shrinking the data transfer to 8K;
- js/index.php (or implicitly as "js/") can also act as a proxy to piwik.php;
- If you are concerned about the impact of browser-based privacy filters which attempt to block tracking, you can change your tracking code to use "js/" instead of "piwik.js" and "piwik.php", respectively.

https://github.com/matomo-org/matomo/blob/3.x-dev/js/README.md

Whenever we already deal with a User object, let's use the more specific
method avatar_icon_for_user.

From https://gitlab.com/gitlab-org/gitlab-ce/issues/36760

Was reverted in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14373

Signed-off-by: Rémy Coutable <remy@rymai.me>

Adds `#build_notification_recipients` to `NotificationRecipientService`
that returns the `NotificationRecipient` objects in order to be able to
access the new attribute `reason`.

This new attribute is used in the different notifier methods in order to
add the reason as a header: `X-GitLab-NotificationReason`.

Only the reason with the most priority gets sent.

Calling `finder.execute.count` twice will perform two queries, but these are all
in the same file, so it's easy to just reuse them.

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/40825

Closes #40824