Bridge: make some headers submissions free (#4102)

supersedes https://github.com/paritytech/parity-bridges-common/pull/2873

Draft because of couple of TODOs:
- [x] fix remaining TODOs;
- [x] double check that all changes from
https://github.com/paritytech/parity-bridges-common/pull/2873 are
correctly ported;
- [x] create a separate PR (on top of that one or a follow up?) for
https://github.com/paritytech/polkadot-sdk/tree/sv-try-new-bridge-fees;
- [x] fix compilation issues (haven't checked, but there should be
many).

---------

Co-authored-by: Adrian Catangiu <adrian@parity.io>

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

@@ -7,17 +7,31 @@ source "$FRAMEWORK_PATH/utils/zombienet.sh"
 
 rococo_dir=$1
 westend_dir=$2
-__relayer_pid=$3
+__finality_relayer_pid=$3
+__parachains_relayer_pid=$4
+__messages_relayer_pid=$5
 
 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" $relayer_log relayer_pid
+# start finality relayer
+finality_relayer_log=$logs_dir/relayer_finality.log
+echo -e "Starting rococo-westend finality relayer. Logs available at: $finality_relayer_log\n"
+start_background_process "$helper_script run-finality-relay" $finality_relayer_log finality_relayer_pid
+
+# start parachains relayer
+parachains_relayer_log=$logs_dir/relayer_parachains.log
+echo -e "Starting rococo-westend parachains relayer. Logs available at: $parachains_relayer_log\n"
+start_background_process "$helper_script run-parachains-relay" $parachains_relayer_log parachains_relayer_pid
+
+# start messages relayer
+messages_relayer_log=$logs_dir/relayer_messages.log
+echo -e "Starting rococo-westend messages relayer. Logs available at: $messages_relayer_log\n"
+start_background_process "$helper_script run-messages-relay" $messages_relayer_log messages_relayer_pid
 
 run_zndsl ${BASH_SOURCE%/*}/rococo.zndsl $rococo_dir
 run_zndsl ${BASH_SOURCE%/*}/westend.zndsl $westend_dir
 
-eval $__relayer_pid="'$relayer_pid'"
-
+eval $__finality_relayer_pid="'$finality_relayer_pid'"
+eval $__parachains_relayer_pid="'$parachains_relayer_pid'"
+eval $__messages_relayer_pid="'$messages_relayer_pid'"