A struct representing an attachment.
Nylas docs
@type t() :: %ExNylas.Attachment{ content_disposition: String.t() | nil, content_id: String.t() | nil, content_type: String.t() | nil, filename: String.t() | nil, grant_id: String.t() | nil, id: String.t() | nil, is_inline: boolean() | nil, size: non_neg_integer() | nil }