Server should be able to pick the reduction from a list

[xballoy]

Currently in the configuration file we can put only one type of reduction at the time (see reduction configuration). We should be able to use an array of reductions.

Definition of done

• Replace the "reduction" field by an array in the configuration file
• If the picked reduction is not known we fallback to "STANDARD" (current behaviour) to prevent crash from typo in the config file.
• Add tests

To be discussed

• Do we randomly pick a reduction or we can weight them?

[annemano]

I'll do this one!

And then adding weight could be done in a separate PR.