Support IO with single age groups

[charlie0614]

Motivation / Current Behaviour

No response

Enhancement description

We should adjust the framework to easily read in age-aggregated but spatially resolved data to create a graph-model with single age groups.
Regarding the ODE models, this needs to be done in the

• ODE SECIR model (done in 1315 support IO functionality with single age group for ODE SECIR #1354 )
• ODE SECIRVVS model
• ODE Secirts model

Additional context

No response

Checklist

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