Add WALSummarizerLock to wait_event_names.txt

Per report from Nathan Bossart.

Discussion: http://postgr.es/m/20231227153647.GA601861@nathanxps13

src/backend/utils/activity/wait_event_names.txt

@@ -324,6 +324,7 @@ XactTruncation	"Waiting to execute <function>pg_xact_status</function> or update
 WrapLimitsVacuum	"Waiting to update limits on transaction id and multixact consumption."
 NotifyQueueTail	"Waiting to update limit on <command>NOTIFY</command> message storage."
 WaitEventExtension	"Waiting to read or update custom wait events information for extensions."
+WALSummarizerLock	"Waiting to read or update WAL summarization state."
 
 XactBuffer	"Waiting for I/O on a transaction status SLRU buffer."
 CommitTsBuffer	"Waiting for I/O on a commit timestamp SLRU buffer."