[FEAT]: Add option for switchable inputs

[wakonig]

Feature Summary

The scan control widget should support switching between input types, e.g. between step size and number of steps. A switchable input widget should be added.

Use Case

Depending on the experiment, it is sometimes more useful to define steps and sometimes step sizes. We should make it optional for the beamlines.

Proposed Solution

The scan signatures will have to be adapted to support exclusive inputs.