Blockchain watchdogs use unique actor name (#1667)

Actor names cannot conflict.

Even though blockchain watchdog actors stop themselves after fetching block
data, when blocks are found in a short interval, we may end up with multiple
actors of the same type simultaneously alive, so we need them to have
unique names.

The blockcount isn't sufficient to make their names unique because forks
can happen.

Fixes #1665

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/watchdogs/BlockchainWatchdog.scala

@@ -23,6 +23,7 @@ import fr.acinq.bitcoin.{BlockHeader, ByteVector32}
 import fr.acinq.eclair.blockchain.CurrentBlockCount
 import fr.acinq.eclair.blockchain.watchdogs.Monitoring.{Metrics, Tags}
 
+import java.util.UUID
 import scala.concurrent.duration.{DurationInt, FiniteDuration}
 import scala.util.Random
 
@@ -66,10 +67,11 @@ object BlockchainWatchdog {
             timers.startSingleTimer(CheckLatestHeaders(blockCount), delay)
             Behaviors.same
           case CheckLatestHeaders(blockCount) =>
-            context.spawn(HeadersOverDns(chainHash, blockCount), HeadersOverDns.Source) ! HeadersOverDns.CheckLatestHeaders(context.self)
-            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.BlockstreamExplorer()), "blockstream") ! ExplorerApi.CheckLatestHeaders(context.self)
-            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.BlockcypherExplorer()), "blockcypher") ! ExplorerApi.CheckLatestHeaders(context.self)
-            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.MempoolSpaceExplorer()), "mempool.space") ! ExplorerApi.CheckLatestHeaders(context.self)
+            val id = UUID.randomUUID()
+            context.spawn(HeadersOverDns(chainHash, blockCount), s"${HeadersOverDns.Source}-$blockCount-$id") ! HeadersOverDns.CheckLatestHeaders(context.self)
+            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.BlockstreamExplorer()), s"blockstream-$blockCount-$id") ! ExplorerApi.CheckLatestHeaders(context.self)
+            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.BlockcypherExplorer()), s"blockcypher-$blockCount-$id") ! ExplorerApi.CheckLatestHeaders(context.self)
+            context.spawn(ExplorerApi(chainHash, blockCount, ExplorerApi.MempoolSpaceExplorer()), s"mempool.space-$blockCount-$id") ! ExplorerApi.CheckLatestHeaders(context.self)
             Behaviors.same
           case headers@LatestHeaders(blockCount, blockHeaders, source) =>
             val missingBlocks = blockHeaders match {