BTCPay Extensions Part 2 (#2001)

* BTCPay Extensions Part 2

This PR cleans up the extension system a bit in that:
 * It renames the test extension to a more uniform name
 * Allows yo uto have system extensions, which are extensions but bundled by default with the release (and cannot be removed)
 * Adds a tool to help you generate an extension package from a csproj
 * Refactors the UI extension points to a view component
 * Moves some more interfaces to the Abstractions csproj

* Rename to plugins

BTCPayServer/Controllers/ServerController.Plugins.cs

@@ -0,0 +1,124 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using BTCPayServer.Configuration;
+using BTCPayServer.Contracts;
+using BTCPayServer.Models;
+using BTCPayServer.Plugins;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+
+namespace BTCPayServer.Controllers
+{
+    public partial class ServerController
+    {
+        [HttpGet("server/plugins")]
+        public async Task<IActionResult> ListPlugins(
+            [FromServices] PluginService pluginService,
+            [FromServices] BTCPayServerOptions btcPayServerOptions,
+            string remote = "btcpayserver/btcpayserver-plugins")
+        {
+            IEnumerable<PluginService.AvailablePlugin> availablePlugins;
+            try
+            {
+                availablePlugins = await pluginService.GetRemotePlugins(remote);
+            }
+            catch (Exception)
+            {
+                TempData.SetStatusMessageModel(new StatusMessageModel()
+                {
+                    Severity = StatusMessageModel.StatusSeverity.Error,
+                    Message = "The remote could not be reached"
+                });
+                availablePlugins = Array.Empty<PluginService.AvailablePlugin>();
+            }
+            var res = new ListPluginsViewModel()
+            {
+                Installed = pluginService.LoadedPlugins,
+                Available = availablePlugins,
+                Remote = remote,
+                Commands = pluginService.GetPendingCommands(),
+                CanShowRestart = btcPayServerOptions.DockerDeployment
+            };
+            return View(res);
+        }
+
+        public class ListPluginsViewModel
+        {
+            public string Remote { get; set; }
+            public IEnumerable<IBTCPayServerPlugin> Installed { get; set; }
+            public IEnumerable<PluginService.AvailablePlugin> Available { get; set; }
+            public (string command, string plugin)[] Commands { get; set; }
+            public bool CanShowRestart { get; set; }
+        }
+
+        [HttpPost("server/plugins/uninstall")]
+        public IActionResult UnInstallPlugin(
+            [FromServices] PluginService pluginService, string plugin)
+        {
+            pluginService.UninstallPlugin(plugin);
+            TempData.SetStatusMessageModel(new StatusMessageModel()
+            {
+                Message = "Plugin scheduled to be uninstalled",
+                Severity = StatusMessageModel.StatusSeverity.Success
+            });
+
+            return RedirectToAction("ListPlugins");
+        }
+        [HttpPost("server/plugins/cancel")]
+        public IActionResult CancelPluginCommands(
+            [FromServices] PluginService pluginService, string plugin)
+        {
+            pluginService.CancelCommands(plugin);
+            TempData.SetStatusMessageModel(new StatusMessageModel()
+            {
+                Message = "Updated",
+                Severity = StatusMessageModel.StatusSeverity.Success
+            });
+
+            return RedirectToAction("ListPlugins");
+        }
+
+        [HttpPost("server/plugins/install")]
+        public async Task<IActionResult> InstallPlugin(
+            [FromServices] PluginService pluginService, string remote, string plugin)
+        {
+            try
+            {
+                await pluginService.DownloadRemotePlugin(remote, plugin);
+                pluginService.InstallPlugin(plugin);
+                TempData.SetStatusMessageModel(new StatusMessageModel()
+                {
+                    Message = "Plugin scheduled to be installed.",
+                    Severity = StatusMessageModel.StatusSeverity.Success
+                });
+            }
+            catch (Exception)
+            {
+                TempData.SetStatusMessageModel(new StatusMessageModel()
+                {
+                    Message = "The plugin could not be downloaded. Try again later.", Severity = StatusMessageModel.StatusSeverity.Error
+                });
+            }
+
+            return RedirectToAction("ListPlugins");
+        }
+
+
+        [HttpPost("server/plugins/upload")]
+        public async Task<IActionResult> UploadPlugin([FromServices] PluginService pluginService,
+            List<IFormFile> files)
+        {
+            foreach (var formFile in files.Where(file => file.Length > 0))
+            {
+                await pluginService.UploadPlugin(formFile);
+                pluginService.InstallPlugin(formFile.FileName.TrimEnd(PluginManager.BTCPayPluginSuffix,
+                    StringComparison.InvariantCultureIgnoreCase));
+            }
+
+            return RedirectToAction("ListPlugins",
+                new {StatusMessage = "Files uploaded, restart server to load plugins"});
+        }
+    }
+}