Move adding of files to the repo helper

Signed-off-by: trivernis <trivernis@protonmail.com>

mediarepo-daemon/mediarepo-database/migrations/20211014184628_add-mime-to-thumbnail.sql

@@ -0,0 +1,3 @@
+-- Add migration script here
+ALTER TABLE thumbnails
+    ADD COLUMN mime VARCHAR(128);

mediarepo-daemon/mediarepo-database/src/entities/thumbnail.rs

@@ -10,6 +10,7 @@ pub struct Model {
     pub hash_id: i64,
     pub height: i32,
     pub width: i32,
+    pub mime: Option<String>,
 }
 
 #[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]