L2: complete CI workflow with real proving

[xqft]

We want to test the whole pipeline and generate real proofs of small blocks.

We can start with #2224 by adding a prover client with the exec backend to the existing integration test, so this workflow would generate fake proofs. We could modify that workflow to test a big amount of transactions.

Then, to close this issue, we can clone that workflow and add one or more prover clients with actual proving, which would need to be run with smaller blocks (so we keep the test time at a sane value).