endpoint_storage: add ?from_endpoint= to /lfc/prewarm (#12195)

Related: https://github.com/neondatabase/cloud/issues/24225
Add optional from_endpoint parameter to allow prewarming from other
endpoint

Cargo.lock

@@ -753,6 +753,7 @@ dependencies = [
  "axum",
  "axum-core",
  "bytes",
+ "form_urlencoded",
  "futures-util",
  "headers",
  "http 1.1.0",
@@ -761,6 +762,8 @@ dependencies = [
  "mime",
  "pin-project-lite",
  "serde",
+ "serde_html_form",
+ "serde_path_to_error",
  "tower 0.5.2",
  "tower-layer",
  "tower-service",
@@ -6422,6 +6425,19 @@ dependencies = [
  "syn 2.0.100",
 ]
 
+[[package]]
+name = "serde_html_form"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d2de91cf02bbc07cde38891769ccd5d4f073d22a40683aa4bc7a95781aaa2c4"
+dependencies = [
+ "form_urlencoded",
+ "indexmap 2.9.0",
+ "itoa",
+ "ryu",
+ "serde",
+]
+
 [[package]]
 name = "serde_json"
 version = "1.0.125"