fix metadata generation paths and integration with Polkadotjs

[failfmi]

Currently, metadata type paths match Rust's metadata paths (they are hard-coded). The problem is that whenever the type paths were switched to Go, the node could not successfully connected to polkadot.js, as the application was written and tested only with Substrate runtimes and probably there are some metadata types generated from paths, which are hard-coded to match the ones from Rust.