feat: add DNSWATCHER_SEND_TEST_NOTIFICATION env var

When set to a truthy value, sends a startup status notification
to all configured notification channels after the first full scan
completes. The notification is clearly an all-ok/success message
showing the number of monitored domains, hostnames, ports, and
certificates.

Closes #84

internal/config/config.go

@@ -38,23 +38,24 @@ type Params struct {
 
 // Config holds application configuration.
 type Config struct {
-	Port              int
-	Debug             bool
-	DataDir           string
-	Domains           []string
-	Hostnames         []string
-	SlackWebhook      string
-	MattermostWebhook string
-	NtfyTopic         string
-	DNSInterval       time.Duration
-	TLSInterval       time.Duration
-	TLSExpiryWarning  int
-	SentryDSN         string
-	MaintenanceMode   bool
-	MetricsUsername   string
-	MetricsPassword   string
-	params            *Params
-	log               *slog.Logger
+	Port                 int
+	Debug                bool
+	DataDir              string
+	Domains              []string
+	Hostnames            []string
+	SlackWebhook         string
+	MattermostWebhook    string
+	NtfyTopic            string
+	DNSInterval          time.Duration
+	TLSInterval          time.Duration
+	TLSExpiryWarning     int
+	SentryDSN            string
+	MaintenanceMode      bool
+	MetricsUsername      string
+	MetricsPassword      string
+	SendTestNotification bool
+	params               *Params
+	log                  *slog.Logger
 }
 
 // New creates a new Config instance from environment and config files.
@@ -105,6 +106,7 @@ func setupViper(name string) {
 	viper.SetDefault("MAINTENANCE_MODE", false)
 	viper.SetDefault("METRICS_USERNAME", "")
 	viper.SetDefault("METRICS_PASSWORD", "")
+	viper.SetDefault("SEND_TEST_NOTIFICATION", false)
 }
 
 func buildConfig(
@@ -143,23 +145,24 @@ func buildConfig(
 	}
 
 	cfg := &Config{
-		Port:              viper.GetInt("PORT"),
-		Debug:             viper.GetBool("DEBUG"),
-		DataDir:           viper.GetString("DATA_DIR"),
-		Domains:           domains,
-		Hostnames:         hostnames,
-		SlackWebhook:      viper.GetString("SLACK_WEBHOOK"),
-		MattermostWebhook: viper.GetString("MATTERMOST_WEBHOOK"),
-		NtfyTopic:         viper.GetString("NTFY_TOPIC"),
-		DNSInterval:       dnsInterval,
-		TLSInterval:       tlsInterval,
-		TLSExpiryWarning:  viper.GetInt("TLS_EXPIRY_WARNING"),
-		SentryDSN:         viper.GetString("SENTRY_DSN"),
-		MaintenanceMode:   viper.GetBool("MAINTENANCE_MODE"),
-		MetricsUsername:   viper.GetString("METRICS_USERNAME"),
-		MetricsPassword:   viper.GetString("METRICS_PASSWORD"),
-		params:            params,
-		log:               log,
+		Port:                 viper.GetInt("PORT"),
+		Debug:                viper.GetBool("DEBUG"),
+		DataDir:              viper.GetString("DATA_DIR"),
+		Domains:              domains,
+		Hostnames:            hostnames,
+		SlackWebhook:         viper.GetString("SLACK_WEBHOOK"),
+		MattermostWebhook:    viper.GetString("MATTERMOST_WEBHOOK"),
+		NtfyTopic:            viper.GetString("NTFY_TOPIC"),
+		DNSInterval:          dnsInterval,
+		TLSInterval:          tlsInterval,
+		TLSExpiryWarning:     viper.GetInt("TLS_EXPIRY_WARNING"),
+		SentryDSN:            viper.GetString("SENTRY_DSN"),
+		MaintenanceMode:      viper.GetBool("MAINTENANCE_MODE"),
+		MetricsUsername:      viper.GetString("METRICS_USERNAME"),
+		MetricsPassword:      viper.GetString("METRICS_PASSWORD"),
+		SendTestNotification: viper.GetBool("SEND_TEST_NOTIFICATION"),
+		params:               params,
+		log:                  log,
 	}
 
 	return cfg, nil