`docs.rs` build fails due to readonly filesystem

[pileks]

Looking at the latest docs.rs build, our Rust docs builds fail due to us compiling and serializing our WASM modules used in the default config.

Offending file: packages/default-config/build.rs, line 17

We should probably detect whether we're inside of a docs.rs build, and if we are, skip serializing these files. They shouldn't impact the generated docs.

How to detect docs.rs build:
https://docs.rs/about/builds