feat: add group duty pin notification feature

- Introduced a new configuration option `DUTY_PIN_NOTIFY` to control whether the bot re-pins the duty message when updated, providing notifications to group members.
- Updated the architecture documentation to reflect the new functionality of re-pinning duty messages.
- Enhanced the `.env.example` file to include the new configuration option with a description.
- Added tests to verify the behavior of the new refresh pin command and its integration with the existing group duty pin functionality.
- Updated internationalization messages to include help text for the new `/refresh_pin` command.

duty_teller/config.py

@@ -64,6 +64,7 @@ class Settings:
     external_calendar_ics_url: str
     duty_display_tz: str
     default_language: str
+    duty_pin_notify: bool
 
     @classmethod
     def from_env(cls) -> "Settings":
@@ -108,6 +109,8 @@ class Settings:
             duty_display_tz=os.getenv("DUTY_DISPLAY_TZ", "Europe/Moscow").strip()
             or "Europe/Moscow",
             default_language=normalize_lang(os.getenv("DEFAULT_LANGUAGE", "en")),
+            duty_pin_notify=os.getenv("DUTY_PIN_NOTIFY", "1").strip().lower()
+            not in ("0", "false", "no"),
         )
 
 
@@ -128,6 +131,7 @@ CORS_ORIGINS = _settings.cors_origins
 EXTERNAL_CALENDAR_ICS_URL = _settings.external_calendar_ics_url
 DUTY_DISPLAY_TZ = _settings.duty_display_tz
 DEFAULT_LANGUAGE = _settings.default_language
+DUTY_PIN_NOTIFY = _settings.duty_pin_notify
 
 
 def is_admin(username: str) -> bool: