Feature: support threads for telegram notifications

[dotX12]

First of all I want to say thank you for this project.

I have a big request to add support for threads for notifications using telegram.
Add an optional thread_id field that will influence which thread a telegram message will go to in a channel/chat.

In a recent (or long ago) update, it was possible to create threads in a telegram group, and to send a message to a specific thread, you need to specify message_thread_id

Example:

curl -X POST -H 'Content-Type: application/json' \
  -d '{"message_thread_id": "4", "chat_id": "-100_<chat_id>", "text": "some message"}' \
  https://api.telegram.org/bot<BOT_TOKEN>/sendMessage

[vmihailenco]

Sure thing, will add.

We're in the middle of a big refactoring so this will have to wait a bit.