Cleaned up API and added caching

[rimi-itk]

Link to ticket

https://leantime.itkdev.dk/TimeTable/TimeTable?showTicketModal=3534#/tickets/showTicket/3534

Description

• Builds on improvements made in API cleanup #429 by adding caching of API responses
• Adds additional properties in GeoJSON API to make it possible to skip the deltag.aarhus.dk → Carto → deltag.aarhus.dk loop for showing stuff on a map – which we do.

Screenshot of the result

Checklist

• My code is covered by test cases.
• My code passes our test (all our tests).
• My code passes our static analysis suite.
• My code passes our continuous integration process.

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