Derek Henry stands on the freshly cut grass of the RDS showgrounds where behind him work is continuing on the interiors of its nearly complete new €59 million arena. Dozens of workers are putting the finishing touches to the three-storey stand ahead of its official debut on August 5, the first day of the Dublin Horse Show.  Henry, chief executive of Gallagher Ireland, a subsidiary of the global insurance giant, has just inked a deal to become title sponsor of Ireland’s premier equine event. It started in 1864 and attracts 100,000 visitors annually. “Sponsorship is part of our DNA in…