Bridge zombienet tests - move all test scripts to the same folder (#3333)

Related to https://github.com/paritytech/polkadot-sdk/issues/3242

bridges/testing/environments/rococo-westend/start_relayer.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+set -e
+
+source "${BASH_SOURCE%/*}/../../utils/common.sh"
+source "${BASH_SOURCE%/*}/../../utils/zombienet.sh"
+
+rococo_dir=$1
+westend_dir=$2
+__relayer_pid=$3
+
+logs_dir=$TEST_DIR/logs
+helper_script="${BASH_SOURCE%/*}/helper.sh"
+
+relayer_log=$logs_dir/relayer.log
+echo -e "Starting rococo-westend relayer. Logs available at: $relayer_log\n"
+start_background_process "$helper_script run-relay" $relayer_log relayer_pid
+
+run_zndsl ${BASH_SOURCE%/*}/rococo.zndsl $rococo_dir
+run_zndsl ${BASH_SOURCE%/*}/westend.zndsl $westend_dir
+
+eval $__relayer_pid="'$relayer_pid'"
+