binary size: use shorebird.json instead of shorebird.yaml

[eseidel]

We already have a pre-processing step during flutter build to process shorebird.yaml from its checked in form to its built form. However we could go further and convert it to json. Doing so would allow us to remove more rust dependencies:

├── serde_yaml v0.9.27
│   ├── indexmap v2.1.0 (*)
│   ├── itoa v1.0.10
│   ├── ryu v1.0.16
│   ├── serde v1.0.193 (*)
│   └── unsafe-libyaml v0.2.9

[eseidel]

cargo tree -e normal