Add e2e tests

[heliomar-pena]

Currently all tests are mocked but I think would be good to add some e2e tests to validate when some servers are not working and if needs to be replaced. I think it is not problem to add one e2e test for each translate engine.

The current problem I see is about paid engines, since I would not have token for each one of them so I will not be able to add tests e2e to them because the pipeline will need those paid api keys which I don't have.

So this will be only for free engines