Add chat_id_file configuration parameter for Telegram

[tennisleng]

This PR adds support for reading chat_id from a file, similar to bot_token_file. This allows users to securely pass chat_id using secrets or volumes in docker-compose without exposing it in cleartext in the config file.

Changes

• Added ChatIDFile field to TelegramConfig struct
• Updated validation to require either chat_id or chat_id_file (but not both)
• Added getChatID() method to read chat_id from file
• Updated Notify() method to use the new getChatID() method

Testing

• Follows the same pattern as bot_token_file
• Validates that either chat_id or chat_id_file is provided
• Validates that both are not provided simultaneously
• Reads and parses chat_id from file as int64

Fixes #4672

[TheMeier]

If chat_id is considered a secret it also get mapped to a secret type. Right now it is mapeed to int and is visible unmasked in /#/status

[TheMeier]

related #2498