feat(medusa): Implement the SC migration scripts

[adrien2p]

What Migrate the existing products to the default sales channel

FIXES CORE-434

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Latest commit: d8a4125efa90d20d36225220c6f5a0fa2dc6ce84

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[olivermrbl]

@shahednasser Should be included in an upgrade guide for the release that removes feature flags on Sales Channels. Creating issue for it 👍