[API] Add API backend code

[michelroegl-brunner]

✍️ Description

This PR adds the API code (written in GO) to the repository to create transparancy.

✅ Prerequisites

The following steps must be completed for the pull request to be considered:

• Self-review performed (I have reviewed my code to ensure it follows established patterns and conventions.)
• Testing performed (I have thoroughly tested my changes and verified expected functionality.)

🛠️ Type of Change

Please check the relevant options:

• [] Bug fix (non-breaking change that resolves an issue)
• New feature (non-breaking change that adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change unexpectedly)
• [] New script (a fully functional and thoroughly tested script or set of scripts)

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📋 Additional Information (optional)

Provide any extra context or screenshots about the feature or fix here.

[CrazyWolf13]

lgtm, awesome that this is added :)

[michelroegl-brunner]

Yep, its part of the Project and should be here. And probably there is someone out there how writes better Go than me and can optimize it^^