Feat/usage stats collection (#317)

* feat: implement anonymous usage data collection

Co-authored-by: Joseph Milazzo <joseph.v.milazzo@gmail.com>

API/Data/FileRepository.cs

@@ -0,0 +1,35 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using API.Interfaces;
+using Microsoft.EntityFrameworkCore;
+
+namespace API.Data
+{
+    public class FileRepository : IFileRepository
+    {
+        private readonly DataContext _dbContext;
+
+        public FileRepository(DataContext context)
+        {
+            _dbContext = context;
+        }
+
+        public async Task<IEnumerable<string>> GetFileExtensions()
+        {
+            var fileExtensions = await _dbContext.MangaFile
+                .AsNoTracking()
+                .Select(x => x.FilePath)
+                .Distinct()
+                .ToArrayAsync();
+
+            var uniqueFileTypes = fileExtensions
+                .Select(Path.GetExtension)
+                .Where(x => x is not null)
+                .Distinct();
+
+            return uniqueFileTypes;
+        }
+    }
+}