add custom bytes range query to cookbook

[andunieee]

Related issue

Fixes #346 (comment)

What does this PR do?

• adds an example of how to use a custom RangeBounds implementation with Vec<u8> keys to the cookbook.

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• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
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[Kerollmops]

Thank you very much for your PR, very appreciated.

[Kerollmops]

That's very nice! Thank you very much 👍 Would you mind fixing the example, please?

[Kerollmops]

Nice! Thank you! Merging 😇