Commit NR tests

A Non Regression test already exists but it has not been committed yet as its baseseline requires 3.2Gb of input data (which we'll need to archive in case data providers can't provide the data), plus 920Mb of reference data.

Also, at this time, metadata NR isn't tested.

• Register the ~ 5Gb of baseline for NR test
• And implement data retrieval (if not in cache)
• Use diff <(gdalinfo baseline/image) <(gdalinfo testout/image) to test metadata NR