Support Intel GPU metrics similar to nvtop

[kaidelorenzo]

Has this issue been covered in the Wiki?

• I have read the Wiki and my issue is not covered.

Is there an existing issue reported already?

• I have searched the existing issues, it does not exist.

Describe the new feature you would like

It would be useful if the extension displayed GPU load and frequency usage for Intel GPUs.

Additional context

I know this gets requested a lot, but in the case of Intel GPUs there are some details exposed in the kernel:

/sys/class/drm/card1/gt*: has GPU clock information
^ this can also be read through udev

usage can be computed from active process time on the GPU

nvtop has an implementation of both of these

nvtop Intel support

There is a similar issue for AMD GPUs #124

Obviously this will all be easier and more feature complete when Intel adds more details into the kernel