Add "dxdiag" to keywords for graphical_information KCMs

Since the previous change about winver (!271 (merged)) was so well-received, I decided to add another useful keyword, thanks to this comment from Phoronix forums that kindly suggested it:

Seriously, what the fuck. KDE is not Windows. Linux not Windows.

I'm amazed, yet again, that this kind of bullshit reasoning wins these days and makes it in. Why not add dxdiag too? Or hey, why not the windows shutdown commands > too (with the /r, /o /whatever). Because, hey, muscle memory..... I'm sure admins would love active directory in linux too, so why not add that as well.

Garbage reasoning.

These things would be nice for april fools... At least then it's a joke.

And why not indeed: the tool is often used/suggested on Windows as the one place to grab information about connected displays, their capabilities, current resolution/refresh rate, the driver and its version in use. It is often used to check if the GPU meets the minimum DirectX version for some application, just like some minimum version of Vulkan might similarly be required on Linux.

Preview screenshot of DxDiag on Display tab:

Hence it makes sense to pull up things from KInfoCenter's Graphics category when someone is searching for dxdiag. And it's easy to imagine why someone could try it: for a pretty new user to KDE, they might not be aware that Info Center is an utility that exists and contains similar information, so they might end up on a lengthy/frustrating quest of finding random CLI tools to pull some of this information up (and perhaps come across outdated info about X11 display server while they're using Wayland and so on), while it's all right there in a single place! So as a last ditch effort, not knowing where to even start, they might type in dxdiag into the search bar, and bam! – they actually arrived at what they wanted.

Another situation is when someone, say a Steam Deck user, is asked by someone, say game's tech support, to "pull up dxdiag" and tell them some information like their GPU or screen resolution. And now they might be in for a pleasant surprise that they'll be directed to some place by KRunner with this MR as well. This will be a substantial improvement over current situation where such a user would type in dxdiag and end up finding random dxdiag.exe from random WINE/Proton prefixes, which would not help them much.

There's also System, Sound and Input sections, but those are not important there, as the tool usually isn't pulled up for that specifically – and if someone ends up in Info Center already, they'll easily find the appropriate sections for this kind of info as well then.

(note: the remainder of the suggestions from the comment are not applicable — shutdown is a CLI command and it already exists in Linux; Active Directory in Linux exists already too: it's called Samba and has been around for a while as well)