(CNN) – The Republican mayor of San Diego has announced plans to air an ad advocating for same-sex marriage rights during next week's Republican National Convention in Tampa. The spot, titled "Family and Freedom," comes after the Republican Party developed its official plank on gay marriage, which pushes for a federal constitutional amendment banning same-sex couples from marriage. The platform is expected to be officially confirmed at the convention next week. The Human Rights Campaign and Freedom to Marry said they will run the spot from Monday through Thursday next week in a $30,000 television ad buy in the Tampa...