Sienna Miller, the heroine of hackgate, is pregnant with her first child. Miller is also reportedly engaged to Tom Sturridge, the baby daddy. 29-year-old Miller started dating 26-year-old Sturridge last March after ending her relationship with on-again, off-again ex-boyfriend Jude Law. Sienna’s sister, fashion designer Savannah, confirmed the news on Twitter. Savannah tweeted ‘THRILLED’ about …