Add configurable SMTP TLS/SSL options (#5204)

## Summary
- add optional STARTTLS and SSL-related fields to mail settings with
defaults matching prior behavior
- apply the new mail properties in the SMTP JavaMail configuration,
including trust and hostname verification overrides
- update mail settings template and tests to cover default behavior and
explicit TLS/SSL overrides
- clarify STARTTLS naming and sslTrust usage with examples in property
comments and the settings template
- default sslTrust to a wildcard when unset so TLS connections accept
any host by default unless tightened

## Testing
- ./gradlew :proprietary:test --tests
stirling.software.proprietary.security.service.MailConfigTest --console
plain

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[Codex
Task](https://chatgpt.com/codex/tasks/task_b_693864b2a6648328ae75c7e88a726a65)

app/common/src/main/java/stirling/software/common/model/ApplicationProperties.java

@@ -574,6 +574,16 @@ public class ApplicationProperties {
         private String username;
         @ToString.Exclude private String password;
         private String from;
+        // STARTTLS upgrades a plain SMTP connection to TLS after connecting (RFC 3207)
+        private Boolean startTlsEnable = true;
+        private Boolean startTlsRequired;
+        // SSL/TLS wrapper for implicit TLS (typically port 465)
+        private Boolean sslEnable;
+        // Hostnames or patterns (e.g., "smtp.example.com" or "*") to trust for TLS certificates;
+        // defaults to "*" (trust all) when not set
+        private String sslTrust;
+        // Enables hostname verification for TLS connections
+        private Boolean sslCheckServerIdentity;
     }
 
     @Data