Support telegram notifications

[0xfornax]

The user needs to create a bot from https://t.me/BotFather. This will create the bot and give you the Bot Token. You'll need the token and a chat id where the bot is present (either a group chat or a dm).

If you want to have a DM with the bot send a /start message and then check the URL https://api.telegram.org/bot<YOUR_BOT_TOKEN>/getUpdates

You should get a response like

"chat": {
  "id": 123456789,
  "type": "private"
}

This is the id you should set on the Telegram Chat ID field.

Closes #472

[github-actions]

Coverage Report

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/rocket-pool/smartnode/rocketpool-cli/service/config	0.00% (ø)
github.com/rocket-pool/smartnode/shared/services/config	2.90% (+0.04%)	👍

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/rocket-pool/smartnode/rocketpool-cli/service/config/settings-alerting.go	0.00% (ø)	900 (+41)	0	900 (+41)
github.com/rocket-pool/smartnode/shared/services/config/alertmanager-config.go	3.88% (+1.45%)	670 (+135)	26 (+13)	644 (+122)	👍

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/rocket-pool/smartnode/shared/services/config/alertmanager-config_test.go