Add Iroh relay mode config

Cargo.lock

@@ -1090,6 +1090,7 @@ dependencies = [
  "directories",
  "serde",
  "thiserror 2.0.18",
+ "toml_edit",
 ]
 
 [[package]]
@@ -3860,6 +3861,7 @@ dependencies = [
  "indexmap",
  "toml_datetime",
  "toml_parser",
+ "toml_writer",
  "winnow",
 ]
 
@@ -3872,6 +3874,12 @@ dependencies = [
  "winnow",
 ]
 
+[[package]]
+name = "toml_writer"
+version = "1.1.1+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "756daf9b1013ebe47a8776667b466417e2d4c5679d441c26230efd9ef78692db"
+
 [[package]]
 name = "tower"
 version = "0.5.3"