getThreadReplies reads a parent message and its thread replies. Slack identifies
the thread with the parent message’s timestamp, exposed here as
threadTimestamp.
Example
automations/read-slack-thread.automation.ts
Inputs
Output
Returnsmessages: SlackMessage[], hasMore, and pagination
responseMetadata.nextCursor. Preserve conversationId together with message
timestamps: timestamps are only meaningful as message identifiers inside their
conversation.