Reuse more code when read in data in model specific IO files

[HenrZu]

Motivation / Current Behaviour

A lot of code used to read data , e.g., read_population_data, is doubled in the parameters_io files for the ODE models. We should add documentation and also make them generic.

Enhancement description

less code would make it easier to maintain.

Additional context

No response

Checklist

• [X] Attached labels, especially loc:: or model:: labels.
• [X] Linked to project