Add proxy support for telegram_bot (home-assistant#8717)

* Add proxy support for telegram_bot

New optional config parameters `proxy_url` and `proxy_params` (a dict)
```yaml
telegram_bot:
  platform: polling
  api_key: !secret telegram_bot_api_key
  allowed_chat_ids:
    - !secret telegram_bot_chatid
  proxy_url: socks5://proxy_ip:proxy_port
  proxy_params:
    username: my-username
password: my-secret-password
```

* change `ATTR_` for `CONF_` for config params

homeassistant/components/telegram_bot/__init__.py

@@ -59,6 +59,8 @@
 ATTR_USERNAME = 'username'
 
 CONF_ALLOWED_CHAT_IDS = 'allowed_chat_ids'
+CONF_PROXY_URL = 'proxy_url'
+CONF_PROXY_PARAMS = 'proxy_params'
 
 DOMAIN = 'telegram_bot'
 
@@ -85,6 +87,8 @@
     vol.Required(CONF_ALLOWED_CHAT_IDS):
         vol.All(cv.ensure_list, [vol.Coerce(int)]),
     vol.Optional(ATTR_PARSER, default=PARSER_MD): cv.string,
+    vol.Optional(CONF_PROXY_URL): cv.string,
+    vol.Optional(CONF_PROXY_PARAMS): dict,
 })
 
 BASE_SERVICE_SCHEMA = vol.Schema({
@@ -240,7 +244,9 @@ def async_setup(hass, config):
         hass,
         p_config.get(CONF_API_KEY),
         p_config.get(CONF_ALLOWED_CHAT_IDS),
-        p_config.get(ATTR_PARSER)
+        p_config.get(ATTR_PARSER),
+        p_config.get(CONF_PROXY_URL),
+        p_config.get(CONF_PROXY_PARAMS)
     )
 
     @asyncio.coroutine
@@ -303,18 +309,24 @@ def _render_template_attr(data, attribute):
 class TelegramNotificationService:
     """Implement the notification services for the Telegram Bot domain."""
 
-    def __init__(self, hass, api_key, allowed_chat_ids, parser):
+    def __init__(self, hass, api_key, allowed_chat_ids, parser,
+                 proxy_url=None, proxy_params=None):
         """Initialize the service."""
         from telegram import Bot
         from telegram.parsemode import ParseMode
+        from telegram.utils.request import Request
 
         self.allowed_chat_ids = allowed_chat_ids
         self._default_user = self.allowed_chat_ids[0]
         self._last_message_id = {user: None for user in self.allowed_chat_ids}
         self._parsers = {PARSER_HTML: ParseMode.HTML,
                          PARSER_MD: ParseMode.MARKDOWN}
         self._parse_mode = self._parsers.get(parser)
-        self.bot = Bot(token=api_key)
+        request = None
+        if proxy_url is not None:
+            request = Request(proxy_url=proxy_url,
+                              urllib3_proxy_kwargs=proxy_params)
+        self.bot = Bot(token=api_key, request=request)
         self.hass = hass
 
     def _get_msg_ids(self, msg_data, chat_id):