REST API: support creating replies and a full reply hierarchy

[iTerminate]

While adding a reply-tree view to bely-cli's TUI, found two gaps in the REST API around log entry replies. The DB already supports both (Log.parentLog / Log.childLogList is an arbitrary-depth tree), and the JSF portal already creates replies via ItemDomainLogbookController.prepareAddLogReply, but this isn't reachable over /api.

• Support creating a reply via the API. PUT /api/Logbook/AddUpdateLogEntry (LogbookRoute.addUpdateLogEntry) can only create top-level entries — the LogEntry DTO has no parent field. Add a parentLogId field to rest/entities/LogEntry.java, and branch in addUpdateLogEntry (when logId is null and parentLogId is set) to build the entry the same way ItemDomainLogbookController.prepareAddLogReply does: LogUtility.createLogEntry(user) + setParentLog(parentLog), not ItemDomainLogbookControllerUtility.prepareAddLog (which would wire it into the document's own item-element list and make it a top-level entry instead of a reply).
• Support the full reply hierarchy, not just one level. GET /api/Logbook/LogEntries/{logDocumentId}?loadReplies=true only returns direct replies — LogEntry.java's constructor hardcodes false for loadReplies in the recursive call that builds logReplies, so replies-of-replies are silently dropped even though the DB has no such limit.
• Regenerate bely-api (tools/developer_tools/python-client) once both land, so clients (including bely-cli) can pick it up.

Prerequisite for bely-cli's reply-tree viewer to support composing a reply and to correctly render nested threads deeper than one level.