Add CLI functionality to remove duplicated collections form RfHub2

[MaciejWiczk]

When doing an internal training on RfHub2 I was pointed, that removing duplicated entries would be beneficial for users. This could utilize similar feature as update/merge mode when looking for duplicated/existing collections or an approach mentioned in this feature. Duplicates removal should be triggered with CLI using command: rfhub2-cli --mode=deduplicate or: rfhub2-cli --mode=remove-deduplicates or any better name to reflect what the app is doing ;)