build(docs): Move static webapp config (microsoft#23116)

Publishing step needs this config to live in the build output directory.
Placing it under `static` ensures it is copied to the right place.

See Azure/static-web-apps#1071 for more
details.

Confirmed that the swa-cli is able to find this when run locally. This
is also how the site was setup previously, I was just misled by the
documentation leading me to believe that moving it to the root was okay.
It also worked using the local swa-cli tooling 🤷‍♂️