Add SMTP_HELLO_NAME to let operators set the EHLO/HELO identity

Google Workspace SMTP relay (smtp-relay.gmail.com) rejects generic
EHLO identifiers such as "localhost", which is Go net/smtp's default.
Operators can now set SMTP_HELLO_NAME to a valid hostname so that
c.Hello() is called before StartTLS, satisfying strict relay policies.

Fixes https://github.com/getprobo/probo/issues/1284

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/bootstrap/builder.go

@@ -166,6 +166,7 @@ func (b *Builder) Build() (*probodconfig.FullConfig, error) {
 						User:        b.getEnv("SMTP_USER"),
 						Password:    b.getEnv("SMTP_PASSWORD"),
 						TLSRequired: b.getEnvBoolOrDefault("SMTP_TLS_REQUIRED", false),
+						HelloName:   b.getEnv("SMTP_HELLO_NAME"),
 					},
 				},
 				Slack: probodconfig.SlackConfig{