Ability to add DL to invite list (proposed for dilithium-1H)

Give users the ability to add a distribution list to the invitees list.

The issue requests support for adding a distribution list to an invitees list, proposed for dilithium-1H. No files, tests, or entry points are identified, so first locate the invite-list implementation and clarify the expected distribution-list behavior. Done should include a defined workflow for adding a distribution list and validation that it works as intended.

Written by the indexing model from the issue text.