On donor-submission-completed events insert a PK=LPA#random-uuid,SK=#DONOR#PAPER record so we can track the UID has been paid for and checked.

Replaces the use of DonorStore in attorney and certificate provider pages with a new lpastore.ResolvingService that will get the latest data from the store, then add additional data depending on whether it is digital or paper. This returns a new lpastore.Lpa type, so we can ensure that we aren't trying to use data that won't exist for paper applications.

Moves the definition of our various keys to a new file in internal/dynamo.