Further tweak metrics timeline events underneath graphs and on news page

In #24260 (moved) we added metrics timeline events underneath graphs and tweaked those on the news page. While discussing those changes we came up with a couple of improvements that we were unable to implement, because we didn't have the time. Here's the list, in case we find more time for this later on. We should probably create child tickets when starting on one these items.

• Add tooltips to tags explaining them a little more, like "Onion-Routing protocol" for "".
• Make tags clickable by linking them to a page with all events related to that tag.
• Maybe make column headers clickable and as a result sort entries accordingly.
• Maybe change the filtering to only show entries for all countries or all transports on graphs showing users from all countries or using all transports.
• Add annotations to the graph or even mouseovers.
• Add optional JavaScript magic that only displays the first entries and that lets the user expend the list if there are more.
• Find categories or standards for link texts for a more consistent presentation.
• Extend events to graphs in other categories than Users and then add this table there.