improve vm disk performance with VZDiskImageSynchronizationModeFsync

[balajiv113]

Reason
The default disk attachment has a very poor disk performance (mainly when accessed via mmap).

From macOS 12 we have option to set cache and sync mode. Using VZDiskImageSynchronizationModeFsync provides a better performance and best-effort consistency as well.
https://developer.apple.com/documentation/virtualization/vzdiskimagesynchronizationmode/vzdiskimagesynchronizationmodefsync?language=objc

Some results
Commands

#for mmap test
fio --filename=PATH_TO_FILE --direct=1 --rw=randrw --bs=32k --ioengine=mmap --iodepth=256 --runtime=120 --numjobs=4 --time_based --group_reporting --name=iops-test-job --eta-newline=1 --size=1G

#for sync test
fio --filename=PATH_TO_FILE --direct=1 --rw=randrw --bs=32k --ioengine=sync --iodepth=256 --runtime=120 --numjobs=4 --time_based --group_reporting --name=iops-test-job --eta-newline=1 --size=1G

Results
Old
mmap - Read & Write IOPS ~52
sync - Read & write IOPS ~5200

With this PR
mmap - Read & Write IOPS ~3900
sync - Read & write IOPS ~5400

[AkihiroSuda]

Thanks