pass in-feature variables through the config file

[Hsankesara]

Currently, the features in the pipeline does not use any external variable. We can make it more flexible by let the researcher define which variables are modifiable and let the user define those variables in the config file.

For example, in the mock pipeline, we have a feature called steps_per_day. We can make it more flexible for users by letting them provide the time period.

[afolarin]

In principle, we have some information that might be useful in the Specifications https://github.com/RADAR-base/RADAR-Schemas/blob/master/specifications/active/aRMT-1.17.0.yml
but also for the passive streams specifications
https://github.com/RADAR-base/RADAR-Schemas/tree/master/specifications/passive might be a look-up for this type of info.