Connect to mid-sourcing

From a marketing client connection, one can get a client to a mid server

console.log("Connecting to mid server...");
const credentials = await sdk.Credentials.ofExternalAccount(client, "defaultEmailMid");
const midClient = await sdk.init(credentials);

await midClient.client.logon();
const datbaseId = await midClient.getOption("XtkDatabaseId");
console.log("Mid datbaseId: " + datbaseId);
await midClient.NLWS.xtkSession.testCnx();
console.log("Disconnecting from mid");
await midClient.client.logoff();