Support temporary links for local file system provider (#848)

* wip

* Support temporary links for local file system provider

* pass base url to file services

* fix test

* do not crash on errors with local filesystem

* remove console

* fix paranthesis

BTCPayServer/Storage/Services/Providers/FileSystemStorage/TemporaryLocalFileProvider.cs

@@ -0,0 +1,53 @@
+using System;
+using System.IO;
+using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.FileProviders.Physical;
+using Microsoft.Extensions.Primitives;
+using Newtonsoft.Json;
+
+namespace BTCPayServer.Storage.Services.Providers.FileSystemStorage
+{
+    public class TemporaryLocalFileProvider : IFileProvider
+    {
+        private readonly DirectoryInfo _fileRoot;
+        private readonly StoredFileRepository _storedFileRepository;
+        private readonly DirectoryInfo _root;
+
+        public TemporaryLocalFileProvider(DirectoryInfo tmpRoot, DirectoryInfo fileRoot, StoredFileRepository storedFileRepository)
+        {
+            _fileRoot = fileRoot;
+            _storedFileRepository = storedFileRepository;
+            _root = tmpRoot;
+        }
+        public IFileInfo GetFileInfo(string tmpFileId)
+        {
+            tmpFileId =tmpFileId.TrimStart('/', '\\');
+            var path = Path.Combine(_root.FullName,tmpFileId) ;
+            if (!File.Exists(path))
+            {
+                return new NotFoundFileInfo(tmpFileId);
+            }
+
+            var text = File.ReadAllText(path);
+            var descriptor = JsonConvert.DeserializeObject<TemporaryLocalFileDescriptor>(text);
+            if (descriptor.Expiry < DateTime.Now)
+            {
+                File.Delete(path);
+                return new NotFoundFileInfo(tmpFileId);
+            }
+
+            var storedFile = _storedFileRepository.GetFile(descriptor.FileId).GetAwaiter().GetResult();
+            return new PhysicalFileInfo(new FileInfo(Path.Combine(_fileRoot.FullName, storedFile.StorageFileName)));
+        }
+
+        public IDirectoryContents GetDirectoryContents(string subpath)
+        {
+            throw new System.NotImplementedException();
+        }
+
+        public IChangeToken Watch(string filter)
+        {
+            throw new System.NotImplementedException();
+        }
+    }
+}