"[Information Letter 06-14-2021] addressed a narrow question based on the specific representations made by the requesting attorney and the positions taken by the plan involved. It does not purport to address whether call recordings are required to be produced in all cases.... [T]he Letter is not binding on courts or technically even on the DOL itself.... Thus, the courts may take a different view of the particular circumstances addressed in the Letter, or of whether call recordings are subject to production pursuant to the claim regulation in different scenarios."