Add --signature to osxphotos sync

[RhetTbull]

See #1738

Implement the same signature template used in osxphotos import

[oPromessa]

Looking at photo_signature function code I noticed it generates a new fingerprint from the file on disk when:

• photo.fingerprint is not defined
• we're on MacOs

So maybe adding an option on "sync export" to --update-signature-from-file (or a better name) to re-calculate all fingerprints on "sync export" would do the trick?

Would this make sense?

osxphotos/osxphotos/photo_signature.py

Lines 17 to 36 in 4f7895c

	def photo_signature(
	photo: PhotoInfo | PhotoInfoFromFile | dict | str | os.PathLike,
	exiftool: str | None = None,
	) -> str:
	"""Compute photo signature for a PhotoInfo, a PhotoInfo dict, or file path"""
	if isinstance(photo, dict):
	photo = photoinfo_from_dict(photo)
	elif not isinstance(photo, PhotoInfo):
	photo = PhotoInfoFromFile(photo, exiftool=exiftool)
	if photo.shared:
	return _shared_photo_signature(photo)
	if photo.fingerprint:
	return f"{photo.original_filename.lower()}:{photo.fingerprint}"
	if photo.path and is_macos:
	return f"{photo.original_filename.lower()}:{fingerprint(photo.path)}"
	return f"{photo.original_filename.lower()}:{photo.original_filesize}"

[RhetTbull]

This would work but only for photos that are present on disk. If the photos is missing (not downloaded from iCloud) this would fail.