Brian Steinberg Senior TV EditorCBS has set in motion “an external investigation” into allegations of racist and misogynist behavior by senior executives at its local-TV unit, a sign that the ViacomCBS company continues to grapple with these issues even though it has probed them in the recent past.In a memo sent to staffers Friday, George Cheeks, CEO of CBS Entertainment Group, said the company had hired Keisha-Ann Gray, an attorney from the law firm Proskauer Rose, to examine recent