Hide nonce implementation details in metadata (#6562)
See https://github.com/polkadot-fellows/runtimes/issues/248 : using
`TypeWithDefault` having derived `TypeInfo` for `Nonce` causes a
breaking change in metadata for nonce type because it's no longer `u64`.
Adding a default implementation of `TypeInfo` for `TypeWithDefault` to
restore the original type info in metadata.
---------
Co-authored-by: Kian Paimani <[email protected]>