add a EventCacheSize variable to BinlogSyncerConfig to limit the streamer's memory usage

[zing22845]

When the consumption speed of the event chan in streamer cannot catch up with its production speed, leading to an accumulation of events, the current fixed channel size of 10240 might occupy significant memory, potentially triggering an Out Of Memory (OOM) condition. Making the size of the event chan configurable would allow for controlling the memory usage of the streamer.

go-mysql/replication/binlogstreamer.go

Line 90 in f0f8617

s.ch = make(chan *BinlogEvent, 10240)