fix(alerting): Add support for client.insecure in email alerting provider (#583)

* feat: adding client.insecure flag to email configuration

* chore(review): applying suggested changes

---------

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

alerting/provider/email/email.go

@@ -1,11 +1,13 @@
 package email
 
 import (
+	"crypto/tls"
 	"fmt"
 	"math"
 	"strings"
 
 	"github.com/TwiN/gatus/v5/alerting/alert"
+	"github.com/TwiN/gatus/v5/client"
 	"github.com/TwiN/gatus/v5/core"
 	gomail "gopkg.in/mail.v2"
 )
@@ -19,6 +21,9 @@ type AlertProvider struct {
 	Port     int    `yaml:"port"`
 	To       string `yaml:"to"`
 
+	// ClientConfig is the configuration of the client used to communicate with the provider's target
+	ClientConfig *client.Config `yaml:"client,omitempty"`
+
 	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
 	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
 
@@ -62,6 +67,9 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 	m.SetHeader("Subject", subject)
 	m.SetBody("text/plain", body)
 	d := gomail.NewDialer(provider.Host, provider.Port, username, provider.Password)
+	if provider.ClientConfig != nil && provider.ClientConfig.Insecure {
+		d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
+	}
 	return d.DialAndSend(m)
 }