feat(media): use file's sha256 for on-disk name & make directory configurable

In addition, metadata about the file, such as creation time, last access, and
file size, are stored in the database

Cargo.toml

@@ -85,6 +85,9 @@ image = { version = "0.25", default-features = false, features = [
   "jpeg",
   "png",
 ] }
+# Used for creating media filenames
+hex = "0.4"
+sha2 = "0.10"
 # Used to encode server public key
 base64 = "0.22"
 # Used when hashing the state