Rewrite multinode-demo/replicator.sh to avoid fullnode.sh (#5299)

multinode-demo/rpc-url.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+#
+# Given a gossip entrypoint derive the entrypoint's RPC address
+#
+
+entrypoint_address=$1
+if [[ -z $entrypoint_address ]]; then
+  echo "Error: entrypoint address not specified" >&2
+  exit 1
+fi
+
+# TODO: Rather than hard coding, add a `solana-gossip rpc-address` command that
+#       actually asks the entrypoint itself for its RPC address
+echo "http://${entrypoint_address%:*}:8899"