WASM container support

[AFCMS]

https://docs.docker.com/desktop/wasm

Go can be cross compiled to WASM, so it shouldn't be too hard.

OptiPNG may not be usable without much work, maybe it can be disabled for the WASM image at first.

Require using buildbase instead of Alpine for the final WASM image, since Alpine doesn't support WASM.

[AFCMS]

Apparently there is an existing OptiPNG WASM version:

https://github.com/wapm-packages/optipng