Tezt/DAL: Add a migration test for entrapment evidence when the attestation lag changed

What

When the attestation lag changed with protocol change, one should not be able to wrongly denounce the attestation of a trap by considering that an attestation refers to a publication using the new attestation lag instead of the one of the current protocol.

Why

Because otherwise, one could be denounced while they behaved fairly.

How

Adding a migration test for this case.

Manually testing the MR

One can run:

make && dune exec tezt/tests/main.exe -- --file tezt/tests/dal.ml migration dal attestation_lag alpha --log-file /tmp/exp_$(date "+%Hh%M").log