Create new UseOqtaneDatabase extension method and replace all uses of UseSqlServer.

This is a preparative step to locate all database configuration in one file.

Oqtane.Server/Extensions/DbContextOptionsBuilderExtensions.cs

@@ -0,0 +1,15 @@
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.EntityFrameworkCore;
+
+namespace Oqtane.Extensions
+{
+    public static class DbContextOptionsBuilderExtensions
+    {
+        public static DbContextOptionsBuilder UseOqtaneDatabase([NotNull] this DbContextOptionsBuilder optionsBuilder, string connectionString)
+        {
+            optionsBuilder.UseSqlServer(connectionString);
+
+            return optionsBuilder;
+        }
+    }
+}