[JENKINS-60848] Improve RSS title wording + Add more RSS tests (#4442)

* Add more tests.

Also a little cleanup of RSS.
Fix the broken "All all ..." title and description.
Remove a long unused bit for never implemented trackback.

* Increase date time checks.

* Copy and paste error.

Co-Authored-By: Wadeck Follonier <Wadeck@users.noreply.github.com>

* Assert not empty.

Co-Authored-By: Wadeck Follonier <Wadeck@users.noreply.github.com>

* Add a bunch more tests and clarify title.

Add a number of more tests. Test the various places that RSS is used.
Improve title wording to something consistent and somewhat sensible.

Co-authored-by: Wadeck Follonier <Wadeck@users.noreply.github.com>