feat(wasm): Add support for builtins + uprev to Wasmtime 7

[dotxlem]

This adds support for providing a map of builtin function handlers to a WASM policy module.

I’ve also added support for setting the --capabilities flag in the build script with the OPA_CAPABILITIES environment variable. I normally wouldn’t have included it with this PR however I mistakenly thought it was required to enable builtins in OPA WASM 🙃

Finally, I’ve uprevved to Wasmtime 7 as there is a CVE in 3.0.0 and I happen to use 7 in my own project :)

Usage example:

let mut builtins: HashMap<String, opa::wasm::BuiltinHandler> = Default::default();
builtins.insert(“io.jwt.decode_verify”.to_string(), Box::new(|args| {
    todo!()
    0u32
}));

Opa::new()
    .with_builtins(builtins)
    .build_from_bundle(&bundle)
    .unwrap();