Deliver message reactions in chats of connected business accounts #910

Business bots receive business_message, edited_business_message and deleted_business_messages, but no reactions. When a customer reacts to a message in a chat of a connected business account, the business bot receives nothing, even with message_reaction in allowed_updates (tested on Bot API 10.3).

From the current API:

• MessageReactionUpdated has no business_connection_id, so it can't refer to a business chat.
• BusinessBotRights has no reaction-related right.
• setMessageReaction doesn't accept business_connection_id, so a business bot also can't react on the account's behalf.
• In the MTProto layer, the business updates (updateBotNewBusinessMessage, updateBotEditBusinessMessage, updateBotDeleteBusinessMessage) have no reaction counterpart, and updateBotMessageReaction carries no connection id.

Request

1. Deliver message_reaction updates for chats of connected business accounts, with a business_connection_id field, gated by a new BusinessBotRights flag (for example can_read_reactions).
2. Accept business_connection_id in setMessageReaction.

Use case: customer-service tools built on Telegram Business show the account's conversations in a shared inbox. Customers often answer with a reaction (for example 👍 to confirm an order), and today that answer is invisible to the business bot.