Implement a serializer for user preferences (#336)

Cargo.lock

@@ -1384,6 +1384,7 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_json_path",
+ "serde_urlencoded",
  "serde_yaml",
  "tegen",
  "time",
@@ -1797,6 +1798,18 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "serde_urlencoded"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3491c14715ca2294c4d6a88f15e84739788c1d030eed8c110436aafdaa2f3fd"
+dependencies = [
+ "form_urlencoded",
+ "itoa",
+ "ryu",
+ "serde",
+]
+
 [[package]]
 name = "serde_yaml"
 version = "0.9.34+deprecated"