Fixes: quarkusio#35314

In passing, made the Flyway beans singleton as we access them a lot more
via CDI and we would have created a lot more beans.
Given the comment I removed where the Dependent scope was added, I think
we can consider it is a good move.
I'm aware this means, we will keep Flyway beans around but that's the
price we have to pay to not slow down the initialization too much.

Ideally we wouldn't rely on this but given we had a test relying on it,
better keep this behavior given it doesn't cost much.