Add 'walreceiver-after-ingest' failpoint. Use sleep at this point to imitate slow walreceiver.

Cargo.lock

@@ -552,6 +552,17 @@ dependencies = [
  "termcolor",
 ]
 
+[[package]]
+name = "fail"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec3245a0ca564e7f3c797d20d833a6870f57a728ac967d5225b3ffdef4465011"
+dependencies = [
+ "lazy_static",
+ "log",
+ "rand",
+]
+
 [[package]]
 name = "fallible-iterator"
 version = "0.2.0"
@@ -1289,6 +1300,7 @@ dependencies = [
  "crc32c",
  "crossbeam-utils",
  "daemonize",
+ "fail",
  "futures",
  "hex",
  "hex-literal",