BUG: Pass cycle mode to the trainer for SSL, Crossval_index check

[ant0nsc]

• Add workaround for a bug in PL 1.5.5, see Workaround for bug in PL 1.5.5: CombinedLoader cannot be used with DDP for training data InnerEye-DeepLearning#646
• Fix bug in bounds check for crossvalidation

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