Redesign KubeCon links on the main page

[shurup]

Description

I'm suggesting this redesign of the "Attend KubeCon…" block on the main page (see After):

In my understanding, it's needed since we have five KubeCons now, and adding more huge buttons (as we did before — see Before) won't really work anymore.

While working on this design improvement, I've also noticed a long-standing HTML bug since we had such entities for the KubeCon links for many years: <a href="..." button id="desktopKCButton">. They are not valid for two reasons: a) the <a> tag does not have the button attribute, and b) we can't use the same id for numerous HTML objects on the same page. Thus, I removed the button attribute and converted desktopKCButton from id to class.

Obviously, I've also synced the actual KubeCon events (links & dates) with the upcoming 2025 events.

I've checked how the suggested changes are rendered in two browsers (Firefox and Chrome in Linux). However, more testing, as well as general feedback, will be very much appreciated.

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[sftim]

I think we could use a more comprehensive redesign of our landing page.

This is progress. However, we shouldn't merge this as-is @shurup. Please look at the localized versions of this page; you'll see that the proposed change will break rendering for some (eg Korean).
Can we find a way to make an incremental change that leaves localizations' landing pages looking OK until they have caught up?

[shurup]

Good catch, thank you! I will find a way to keep the "backward compatibility."

P.S. Regarding a more general redesign of this page, I was actually thinking of suggesting some new options to replace that old video (behind the KubeCon links) as my next step...