Finishing up classlib project

Now, we covered the major part of how the class library project should be, let's be more aggressive.

Every model we have, we have a cs file linking to the collection, and we also have a DbConnection cs file.

Extract interface for everyone of them cover all of the actions, just in case some day we want to switch to a different database.

Add the global usings file to wrap up.

global using MongoDB.Driver;
global using MongoDB.Bson;
global using MongoDB.Bson.Serialization.Attributes;
global using Microsoft.Extensions.Caching.Memory;
global using Microsoft.Extensions.Configuration;
global using ThreadsLib.Models;
global using ThreadsLib.DataAccess;