Plugins: Allow creation of independent DbContexts

This allows plugins to create custom dbcontexts, which would be namespaced in the scheme with a prefix. Migrations are supported too and the table would be prefixed too

BTCPayServer.Plugins.Test/Controllers/TestExtensionController.cs

@@ -0,0 +1,35 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using BTCPayServer.Plugins.Test.Data;
+using BTCPayServer.Plugins.Test.Services;
+using Microsoft.AspNetCore.Mvc;
+
+namespace BTCPayServer.Plugins.Test
+{
+    [Route("extensions/test")]
+    public class TestExtensionController : Controller
+    {
+        private readonly TestPluginService _testPluginService;
+
+        public TestExtensionController(TestPluginService testPluginService)
+        {
+            _testPluginService = testPluginService;
+        }
+        
+        // GET
+        public async Task<IActionResult> Index()
+        {
+            return View(new TestPluginPageViewModel()
+            {
+                Data = await _testPluginService.Get()
+            });
+        }
+        
+        
+    }
+
+    public class TestPluginPageViewModel
+    {
+        public List<TestPluginData> Data { get; set; }
+    }
+}