NotificationsService: add telegram

[filimonic]

Add support for notifications using telegram bot.

$Notification/T1=bot_token
$Notification/T2=chat_id
$Notification/Type=TG
$Notification/Send=Hello, World!

---

Memory usage:

Memory type	Before changes	After changes	Difference
RAM	69796	69796	0
Flash	1845089	1845613	⚠️+524

---

Setup:

Obtain bot token:

• Register bot with @BotFather, and get bot token, e.g. 9999999999:ABCdefGHi-JKLmNOpQR-stuvw-xyz012345.

Obtain chat id:

• Choose where you want to get notifications: in personal chat or in group chat.
  • Personal chat: if you want to get notifications to your personal chat, text /start to the bot
  • Group chat: if you want to get notifications to group chat, invite bot to group, text to group chat /nameOfYour_bot hello
• Open https://api.telegram.org/bot{bot-token}/getUpdates in browser and get ..."chat":{"id":-1234567890 here. The number is chat id. Group chats have negative id, personal chats have positive id.

Setup FluidNC with commands:

• $Notification/T1=bot_token, ex, $Notification/T1=9999999999:ABCdefGHi-JKLmNOpQR-stuvw-xyz012345
• $Notification/T2=chat_id, ex, $Notification/T2=-1234567890
• $Notification/Type=TG

Test notification:

• Test notification with command $Notification/Send=Hello, World!

Inject notifications into G-Code:

• For example, add $Notification/Send=Finished to your End G-Code in LightBurn

[MitchBradley]

Based on the rarity of questions about notifications, I suspect that you could count the number of people who use them on one hand. If they are as rarely used as I suspect, I wonder if it makes sense to add yet another variant that is likely to be used by a single person? Perhaps it would be possible to collapse the entire notifications service into a data-driven class that could send arbitrary messages to arbitrary endpoints?