Docs: Accessibility Indicators - Catchments

[UJehle]

### Tasks
- [x] Prepare Structure of page (Ulrike)
- [x] Step-by-Step-Guide Draft (Irem)
- [x] Step-by-Step-Guide Check (Ulrike)
- [x] Step-by-Step-Guide Adjustments (Irem)
- [x] Final Check & Additions (Elias & Ulrike)

[EPajares]

Here are the schemas:

https://github.com/goat-community/goat-core/blob/main/src/schemas/motorized_mobility.py https://github.com/goat-community/goat-core/blob/main/src/schemas/active_mobility.py

The are called IIsochroneActiveMobility AND IIsochroneMotorizedMobility. You can study them and the inherit a lot of dependencies.

[UJehle]

Needs to be finalized when the implementation is done (snyc. with dev-team). Draft-File is saved in OneDrive.

[nihar1024]

TODO:

• [ ] Update car