Can you add an option to ktx create to premultiply image data with alpha and set the flag in DFD?

[jiangzhhhh]

I noticed that the KTX2 specification includes a DFD flag indicating whether image data has already been premultiplied with its alpha channel.
But currently, toktx provides no way to set this flag while also performing the necessary premultiplication on the source image data.
Can add an option to the toktx app (such as -p) to premultiply image data with alpha and set the premultiplied alpha flag in the DFD?​​

[MarkCallow]

Not to toktx, which is deprecated but adding one to ktx create is certainly possible. Happy to accept a PR if you want to create one.