[Glitch] Change media attachment limit to 10000 characters

Port c4ea89dfd952e05da6edd0d47473fd4bd4834dae to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/alt_text_modal/index.tsx

@@ -54,7 +54,8 @@ const messages = defineMessages({
   },
 });
 
-const MAX_LENGTH = 1500;
+// TODO: use `description_limit` from the `/api/v2/instance` response
+const MAX_LENGTH = 10000;
 
 type FocalPoint = [number, number];