provide default implementation for did resolver

[Christiantyemele]

No description provided.

[Christiantyemele]

This issue comes as and adjustment to the current didresolver which i find weird to for a did resolver to take a did document before resolution

#[async_trait]
impl DIDResolver for LocalDIDResolver {
    async fn resolve(&self, did: &str) -> Result<Option<DIDDoc>> {
        if did == self.diddoc.id {
            return Ok(Some(self.diddoc.clone()));
        }

        if !did.starts_with("did:key:") {
            return Err(Error::new(
                ErrorKind::Unsupported,
                DIDResolutionError::MethodNotSupported,
            ));
        }

        let method = DidKey::new_full(true, PublicKeyFormat::Jwk);

        match method.expand(did) {
            Ok(diddoc) => Ok(Some(
                serde_json::from_value(json!(Document {
                    service: Some(vec![]),
                    ..diddoc
                }))
                .expect("Should easily convert between DID document representations."),
            )),
            Err(err) => Err(Error::new(ErrorKind::DIDNotResolved, err)),
        }
    }
}