Add mp4 and webm to nginx config

Mp4 is used by the firstrun plugin. Without these being mentioned in
this section, the firstrun movie isn't shown and the first run modal
dialog apparently can't be closed.

Webm added for completeness as there are files like this in firstrun
assets.

Signed-off-by: Miłosz Kosobucki <milosz@kosobucki.pl>

Author: MiKom

admin_manual/installation/nginx-root.conf.sample

@@ -171,7 +171,7 @@ server {
     }
 
     # Serve static files
-    location ~ \.(?:css|js|mjs|svg|gif|ico|jpg|png|webp|wasm|tflite|map|ogg|flac)$ {
+    location ~ \.(?:css|js|mjs|svg|gif|ico|jpg|png|webp|wasm|tflite|map|ogg|flac|mp4|webm)$ {
         try_files $uri /index.php$request_uri;
         # HTTP response headers borrowed from Nextcloud `.htaccess`
         add_header Cache-Control                     "public, max-age=15778463$asset_immutable";

admin_manual/installation/nginx-subdir.conf.sample

@@ -168,7 +168,7 @@ server {
         }
 
         # Serve static files
-        location ~ \.(?:css|js|mjs|svg|gif|ico|jpg|png|webp|wasm|tflite|map|ogg|flac)$ {
+        location ~ \.(?:css|js|mjs|svg|gif|ico|jpg|png|webp|wasm|tflite|map|ogg|flac|mp4|webm)$ {
             try_files $uri /nextcloud/index.php$request_uri;
             # HTTP response headers borrowed from Nextcloud `.htaccess`
             add_header Cache-Control                     "public, max-age=15778463$asset_immutable";