DID:SOV DIDDoc does resolve without a service/endpoint

[gmulhearn]

part of this series of issues; #1089

in the did_resolver_sov crate, if the did:sov DID does not have an endpoint attribute, then the entire DIDDoc fails to resolve.

E.g. the following fails with NotFound("DID not found"):

#[tokio::test]
async fn write_new_nym_and_get_did_doc() {
    let profile = build_setup_profile().await;
    let (new_nym, verkey) = profile
        .wallet
        .create_and_store_my_did(None, None)
        .await
        .unwrap();

    profile
        .ledger_write
        .publish_nym(
            &profile.wallet,
            &profile.institution_did,
            &new_nym,
            Some(&verkey),
            None,
            None,
        )
        .await
        .unwrap();

    // NEED TO WRITE ENDPOINT FOR IT TO RESOLVE
    // write_test_endpoint(&profile.wallet, &profile.ledger_write, &new_nym).await;

    let resolver = DidSovResolver::new(profile.ledger_read);
    let did = format!("did:sov:{}", new_nym);

    let did_doc = resolver
        .resolve(
            &Did::parse(did.clone()).unwrap(),
            &DidResolutionOptions::default(),
        )
        .await
        .unwrap();

    println!(
        "{}",
        serde_json::to_string_pretty(&did_doc.did_document()).unwrap()
    );
}

Expected behaviour according to spec https://sovrin-foundation.github.io/sovrin/spec/did-method-spec-template.html#crud-operation-definitions :

If an endpoint ATTRIB does not exist for the NYM, the service block is an empty array (e.g. "service": []