refactor(test): make JSON generation smarter by using structs

[vshulcz]

Prerequisites

• I have read and understood the contributing guide.
• The commit message follows the conventional commits guidelines.
• Tests for the changes have been added (for bug fixes / features).
• Docs have been added/updated (for bug fixes / features). (Not applicable as this is a test refactor.)

Description

This PR addresses the TODO: // TODO: make this smarter in the test suite of the Brewfather segment. It seems to me better than the previous implementation with manual JSON concatenation and fmt.Sprintf for formatting.

[JanDeDobbeleer]

@all-contributors please add @vshulcz for code

This is pure magic 🪄! @holopin-bot @vshulcz wizard

[holopin-bot]

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[allcontributors]

@JanDeDobbeleer

I've put up a pull request to add @vshulcz! 🎉