Allow configuring the default fixture set to use

[rimas-kudelis]

sylius:fixtures:load currently has a hardcoded default suite name of default. It would be nice if the default suite used in the absense of an explicit suite argument could be configured via yaml.

[lchrusciel]

Hey Rimas,

the future of this lib is under the question - as @loic425 started the effort of migration of Sylius fixtures into zendstruct foundry. But if we decide to keep this lib alive, your idea would be really good