Add new s3 checksum algorithms to help text

Update --checksum-algorithm help text and choices to include the
SHA512, XXHASH3, XXHASH64, and XXHASH128 algorithms recently added
for S3 object integrity. MD5 is intentionally omitted since it is
only supported for pre-calculated values, not automatic calculation.
Also clarify that the default is 'CRC32' for CLI v1, since CRT is
not guaranteed to be present.

Author: adev-code