Add a `sample_data` module

[sfmig]

Is your feature request related to a problem? Please describe.
It would be good to have a sample_data module to fetch files for our examples (similar to scikit-image

Describe the solution you'd like
An approach like the test data one using pooch should be good and consistent.

Describe alternatives you've considered
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Additional context
We would need to set up a corresponding GIN repository.

[HARSHDIPSAHA]

hi @sfmig , I looked at pr #105 and would like to try completing the sample_data module, should I get working on it?