feat(alerting): Support sending messages to Telegram topics in group (#928)

* feat(alerting): Added the ability to send messages to Telegram topics in groups.

* feat(alerting): Added the ability to send messages to Telegram topics in groups.

fix tests

* feat(alerting): Added the ability to send messages to Telegram topics in groups.

Rename TopicId to TopicID

* feat(alerting): Added the ability to send messages to Telegram topics in groups.

Fixed description for alerting.telegram.topic-id in README.md

---------

Co-authored-by: TwiN <twin@linux.com>

alerting/provider/telegram/telegram.go

@@ -23,9 +23,10 @@ var (
 )
 
 type Config struct {
-	Token  string `yaml:"token"`
-	ID     string `yaml:"id"`
-	ApiUrl string `yaml:"api-url"`
+	Token   string `yaml:"token"`
+	ID      string `yaml:"id"`
+	TopicID string `yaml:"topic-id,omitempty"`
+	ApiUrl  string `yaml:"api-url"`
 
 	ClientConfig *client.Config `yaml:"client,omitempty"`
 }
@@ -53,6 +54,9 @@ func (cfg *Config) Merge(override *Config) {
 	if len(override.ID) > 0 {
 		cfg.ID = override.ID
 	}
+	if len(override.TopicID) > 0 {
+		cfg.TopicID = override.TopicID
+	}
 	if len(override.ApiUrl) > 0 {
 		cfg.ApiUrl = override.ApiUrl
 	}
@@ -117,6 +121,7 @@ type Body struct {
 	ChatID    string `json:"chat_id"`
 	Text      string `json:"text"`
 	ParseMode string `json:"parse_mode"`
+	TopicID   string `json:"message_thread_id,omitempty"`
 }
 
 // buildRequestBody builds the request body for the provider
@@ -150,6 +155,7 @@ func (provider *AlertProvider) buildRequestBody(cfg *Config, ep *endpoint.Endpoi
 		ChatID:    cfg.ID,
 		Text:      text,
 		ParseMode: "MARKDOWN",
+		TopicID:   cfg.TopicID,
 	})
 	return bodyAsJSON
 }