Add traces to measure the time spent in the migration of each document (attachments and versioned documents) in the JCR
Start of the refactoring of the JCR migration in order to fix two important issues: the time taken by the migration and the eventual freeze of the process. AttachmentMigration replaces ComponentAttachmentMigrator and VersioningMigrator replaces ComponentDocumentMigrator
Clean up unused codes and group common code in reusable methods of the DocumentRepository class