Provide alternative mock dataset repositories

[afolarin]

Is your feature request related to a problem? Please describe.
Currently, we only have one mockdata repo, which is optionally cloned as a submodule in the radarpipeline repository. In the future it would be beneficial to have multiple mock data examples (e.g. there may be different examples of wearable data etc.) it would also help to keep the mock data repos to a reasonable size.

Describe the solution you'd like

• change radarpipeline to enable specifying which mock repo it uses
• provide a facility in config.yaml to specify the mock repo required
• add another example e.g mockdata2

Describe alternatives you've considered
An alternative would just be to have mock data repositories and people could use them in the same way as local, local_directory data paths, but just document them as alternative mock datasets.

Additional context