Make aya-build optional

[pythops]

I think the old template using xtask offered some nice functionalities that are missed here.

1. Clean build without the warnings
2. More simple setup (I know this is very subjective)

Some people might not like using xtask and it's fine, they don't need to. I suggest that we give the option to choose between the current setup and the old one with xtask

[vadorovsky]

1. Clean build without the warnings

I think it can be done by tuning the log level in aya-build to INFO or something more appropriate.

3. More simple setup (I know this is very subjective)>
   Some people might not like using xtask and it's fine, they don't need to. I suggest that we give the option to choose between the current setup and the old one with xtask

If someone can make it work with some kind of boolean option in cargo-generate, I would be fine with that.