Fix GIF uploads

This commit fixes GIF uploads and improves GIF support:
- MediaPicker will now skip location data removal processing, as it is not needed on GIF images and causes them to be converted to JPEG images
- The uploader now sets more accurate MIME types on the upload request

Issue Repro
-----------

Device: iPhone 13 Mini
iOS: 17.4.1
Damus: `ada99418f6fcdb1354bc5c1c3f3cc3b4db994ce6`
Steps:
1. Download a GIF from GIPHY to the iOS photo gallery
2. Upload that and attach into a post in Damus
3. Check if GIF is animated.
Results: GIF is not animated. Issue is reproduced.

Testing
-------

PASS

Device: iPhone 13 Mini
iOS: 17.4.1
Damus: this commit
Steps:
1. Create a new post
2. Upload the same GIF as the repro and post
3. Make sure GIF is animated. PASS
4. Create a new post
5. Upload a new GIF image (that has never been uploaded by the user on the app) and post
6. Make sure the GIF is animated on the post. PASS
7. Make sure that JPEGs can still be successfully uploaded. PASS
8. Make sure that MP4s can be uploaded.
9. Make a new post that contains 1 JPEG, 1 MP4 file, and 2 GIF files. Make sure they are all uploaded correctly and all GIF files are animated. PASS

Closes: https://github.com/damus-io/damus/issues/2157
Changelog-Fixed: Fix broken GIF uploads
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Reviewed-by: William Casarin <jb55@jb55.com>

damus/Models/ImageUploadModel.swift

@@ -49,6 +49,32 @@ enum MediaUpload {
         
         return false
     }
+    
+    var mime_type: String {
+        switch self.file_extension {
+            case "jpg", "jpeg":
+                return "image/jpg"
+            case "png":
+                return "image/png"
+            case "gif":
+                return "image/gif"
+            case "tiff", "tif":
+                return "image/tiff"
+            case "mp4":
+                return "video/mp4"
+            case "ogg":
+                return "video/ogg"
+            case "webm":
+                return "video/webm"
+            default:
+                switch self {
+                    case .image:
+                        return "image/jpg"
+                    case .video:
+                        return "video/mp4"
+                }
+        }
+    }
 }
 
 class ImageUploadModel: NSObject, URLSessionTaskDelegate, ObservableObject {