Relativity, a fast-growing Chicago tech company that makes legal software, is naming high-profile techie and LinkedIn veteran Mike Gamson its next CEO. Gamson, who will replace Andrew Sieja, begins his new role July 1. Sieja, Relativity’s founder, will transition to executive chairman. “Relativity is and will always be my life’s work, and I’m excited to bring on a new leader who shares in our vision and commitment to this company,” Sieja said on a conference call with reporters.