Consider updating KTXArtistGuide to not use `toktx`

The [Compression Examples](https://github.com/KhronosGroup/3D-Formats-Guidelines/blob/main/KTXArtistGuide.md#compression-examples) section in the `KTXArtistGuide` refers to several function calls of `toktx`. One could see this as documenting the process that was _actually used_ for generating that specific "StainedGlassLamp" asset. But the `toktx` command has been replaced with specialized commands quite a while ago (see the list at https://github.khronos.org/KTX-Software/ktxtools/index.html ). Maybe this should be updated to use the new commands instead.

Start in KTXArtistGuide.md at the Compression Examples section and review the linked KTX-Software tool list. Determine which specialized commands replace the documented toktx calls, then update the examples so they reflect the current tools and still describe the StainedGlassLamp asset process.

Written by the indexing model from the issue text.