Added interfaces to read and write data in DB and added DbContext implementing these

SchengenVisaApi/Infrastructure/Database/IReader.cs

@@ -0,0 +1,18 @@
+using Domains;
+
+namespace Infrastructure.Database
+{
+    public interface IReader
+    {
+        /// Get all entities of type <typeparamref name="T"/> stored in storage
+        /// <typeparam name="T">Entity type to seek in storage</typeparam>
+        IQueryable<T> GetAll<T>() where T : class, IEntity;
+
+        /// Get one entity with specific <paramref name="id"/> from storage
+        /// <param name="id">Identifier of entity</param>
+        /// <param name="cancellationToken">Cancellation Token</param>
+        /// <typeparam name="T">Type of entity</typeparam>
+        /// <returns>Entity or null if not found</returns>
+        Task<T?> GetOneAsync<T>(Guid id, CancellationToken cancellationToken) where T : class, IEntity;
+    }
+}