Gets reactions for an item.

Optional Params

• channel - Channel where the message to get reactions for was posted.
• file - File to get reactions for.
• file_comment - File comment to get reactions for.
• full - If true always return the complete reaction list.
• timestamp - Timestamp of the message to get reactions for.

Errors the API can return:

• bad_timestamp - Value passed for timestamp was invalid.
• file_comment_not_found - File comment specified by file_comment does not exist.
• file_not_found - File specified by file does not exist.
• message_not_found - Message specified by channel and timestamp does not exist.
• no_item_specified - file, file_comment, or combination of channel and timestamp was not specified.