fix(installer): download correct piper arch

[sammcj]

Doesn't complete resolve #9 as it still seems to try and use Piper AMD64 for some reason, but could be unrelated.

[C-Loftus]

Thanks for adding this here! From what I can tell, upstream piper does not have proper MacOS builds.

rhasspy/piper#284
rhasspy/piper#480
rhasspy/piper#523

I was testing myself on MacOS previously and I also found iconv had a bit different behavior. (Or it could just be something different with how files are encoded). That is the program we use to remove special characters that piper would otherwise speak out literally and mess up the audiobook.

Unfortunately I think using the Docker container might be necessary for the time being. I do have some ideas that I will experiment with but it might be a little bit.

[C-Loftus]

Closing this for the time being since it doesn't appear to work and MacOS appears to be a bit of an issue with piper. If I do add it, I'll probably need to add some helper scripts to fix the binary before using it in piper.