DataIdentfier format change from 40 chars to 64 chars as of JCR-4115

[woonsan]

As of JCR-4115 (https://jira.apache.org/jira/browse/JCR-4115), or since Apache Jackrabbit 2.16.0, the DataIdentifier of DataRecord in DataStore is generated using SHA-256, instead of SHA-1, resulting in 64 chars of identifiers instead of the old 40 chars. When using the same DataStore, this doesn't make any problem as Apache Jackrabbit can read DataRecord with old identifiers.
However, this could make a problem if an old DataStore is migrated in older version to a new version using this tool which is shipped with Apache Jackrabbit 2.16.x or higher because the identifiers are created with different values in target DataStore even for old items in source DataStore. The digest key generation algorithm is hard-coded in CachingDataStore, which is different between pre-2.16 (SHA-1; 40 chars) and 2.16+ (SHA-256; 64 chars).