Add expect enum validation

[arbulu89]

Add expect_enum expectation type validation.
Having one of expect/expect_same/expect_enum entry in the expectation is tested by json schema: trento-project/wanda#374

PD: I have updated the lock file manually. Running the cargo generate-lockfile is including a loooot of changes, so maybe it will be better to do it in a different PR. I hope it is alright.

[dottorblaster]

@arbulu89 it's ok, I'll update the lockfile in another PR if it's too much for you. Just remember that you can rebuild it automatically running cargo build

[arbulu89]

@dottorblaster I can perfectly do it in this PR. It doesn't break anything, but it looked to me that it would hide a lot of changes there in this unrelated PR

[dottorblaster]

Thanks! Any further refactoring is deferrable, no worries!