cumulus/client: added external rpc connection retry logic #7514

Job	Run time
set-image	8s
check-runtime-migration (westend)	6m 45s
check-runtime-migration (rococo)	4m 35s
check-runtime-migration (asset-hub-westend)	4m 12s
check-runtime-migration (asset-hub-rococo)	5m 54s
check-runtime-migration (bridge-hub-westend)	3m 45s
check-runtime-migration (bridge-hub-rococo)	3m 40s
check-runtime-migration (contracts-rococo)	3m 52s
check-runtime-migration (collectives-westend)	3m 41s
check-runtime-migration (coretime-rococo)	3m 56s
All runtime migrations passed	1s
	40m 29s

Provide feedback