The investigation into New Orleans Mayor LaToya Cantrell is escalating, along with costs linked to her alleged relationship with a member of her security team. Cantrell has been under investigation by the FBI. New subpoenas have been issued in connection with a federal grand jury that is investigating her, according to NOLA.com, which cited sources familiar with the subpoenas. The investigation includes the extent of the relationship between Cantrell and New Orleans police officer Jeffrey Vappie, according to WVUE-DT. The outlet said that documents it saw showed that a December jaunt to Dubai …