Handles reconnections in external signer

[anhnhgutech]

Is your feature request related to a problem? Please describe.
For now, the SetupExternalSigner only happens once when the node starts.
If it fails, it won't be retried. This means the Clef must be ready before the node starts.

Related to: #6780

Describe the solution you'd like
I checked the flow of geth and nethermind, and I noted the same below:

• geth

flowchart TD
	Start((Start)) --> InitConfiguration[Init Configuration]
	InitConfiguration --> ConnectToExternalSigner[Connect To External Signer]
	ConnectToExternalSigner --> IsConnectSuccess{{Is connect success?}}
	IsConnectSuccess --No --> ThrowError --> End((End))
	IsConnectSuccess --Yes--> ImportBlock[Sync data and import block]
	ImportBlock --> MineBlock[Mine block] --> End
	

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• nethermind

flowchart TD
	Start((Start)) --> InitConfiguration[Init Configuration]
	InitConfiguration --> ConnectToExternalSigner[Connect To External Signer]
	ConnectToExternalSigner --> IsConnectSuccess{{Is connect success?}}
	IsConnectSuccess --No --> SyncDataBlock[Sync data] --> End((End))
	IsConnectSuccess --Yes--> MineBlock[Sync data and mine block] --> End

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In Nethermind, after a failed connection, the node continues running and syncing data without throwing an error. It also doesn't attempt to reconnect at this time. I think we should

• Allow reconnection to the external signer, when the node starts and fails.
• Or throw 1 error (exit with error code)