Remove contention in AsyncUploadCache to improve performance

"qtp838397579-20736" - Thread t@20736
   java.lang.Thread.State: BLOCKED
	at org.apache.jackrabbit.core.data.AsyncUploadCache.hasEntry(AsyncUploadCache.java:165)
	- waiting to lock <4f224235> (a org.apache.jackrabbit.core.data.AsyncUploadCache) owned by "s3-write-worker-14" t@624
	at org.apache.jackrabbit.core.data.CachingDataStore.getRecord(CachingDataStore.java:422)
	at org.apache.jackrabbit.oak.plugins.blob.datastore.DataStoreBlobStore.getDataRecord(DataStoreBlobStore.java:474)
	at org.apache.jackrabbit.oak.plugins.blob.datastore.DataStoreBlobStore.getStream(DataStoreBlobStore.java:463)
	at org.apache.jackrabbit.oak.plugins.blob.datastore.DataStoreBlobStore.getInputStream(DataStoreBlobStore.java:297)
	at org.apache.jackrabbit.oak.plugins.blob.BlobStoreBlob.getNewStream(BlobStoreBlob.java:47)

"s3-write-worker-14" - Thread t@624
   java.lang.Thread.State: RUNNABLE
	at java.io.FileOutputStream.open(Native Method)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:171)
	at org.apache.jackrabbit.core.data.AsyncUploadCache.serializeAsyncUploadMap(AsyncUploadCache.java:293)
	- locked <4f224235> (a org.apache.jackrabbit.core.data.AsyncUploadCache)
	at org.apache.jackrabbit.core.data.AsyncUploadCache.remove(AsyncUploadCache.java:131)
	- locked <4f224235> (a org.apache.jackrabbit.core.data.AsyncUploadCache)