[server] Make sender email configurable (#1696)

Ref:
https://github.com/ente-io/ente/discussions/1582#discussioncomment-9404061

server/configurations/local.yaml

@@ -180,6 +180,9 @@ smtp:
     port:
     username:
     password:
+    # The email address from which to send the email. Set this to an email
+    # address whose credentials you're providing.
+    email:
 
 # Zoho Zeptomail config (optional)
 #

server/pkg/utils/email/email.go

@@ -38,6 +38,7 @@ func sendViaSMTP(toEmails []string, fromName string, fromEmail string, subject s
 	smtpPort := viper.GetString("smtp.port")
 	smtpUsername := viper.GetString("smtp.username")
 	smtpPassword := viper.GetString("smtp.password")
+	smtpEmail := viper.GetString("smtp.email")
 
 	var emailMessage string
 
@@ -50,6 +51,11 @@ func sendViaSMTP(toEmails []string, fromName string, fromEmail string, subject s
 		emailAddresses += email
 	}
 
+	// If an sender email is provided use it instead of the fromEmail.
+	if smtpEmail != "" {
+		fromEmail = smtpEmail
+	}
+
 	header := "From: " + fromName + " <" + fromEmail + ">\n" +
 		"To: " + emailAddresses + "\n" +
 		"Subject: " + subject + "\n" +