Rename config to config.toml

[BrooksCunningham]

Renaming the config file to config.toml to avoid the following warning and potential future error.

✓ Verifying fastly.toml
✓ Checking latest wasm-tools release
✓ Fetching latest wasm-tools release
✓ Identifying package name
✓ Identifying toolchain

WARNING: The Cargo configuration file name is .cargo/config. The file should be renamed to
.cargo/config.toml to be compatible with Rust 1.78.0 or later