Added samples of how to ensure uniqueness in Event Sourcing

[oskardudycz]

Shows how to handle unique constraint checks in an event-sources system. Explains various techniques like:

• talking to business,
• stream id design,
• reservation pattern.

See more in:

• Samples,
• How to ensure uniqueness in Event Sourcing,
• Pull request

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This discussion was created from the release Added samples of how to ensure uniqueness in Event Sourcing.