xcube gen sorts input list and therefore might append wrong time order

[AliceBalfanz]

The order of the appending step of input files to the cube is relevant.
When having input data which has input names first differentiated by e.g. A and B, the input files are sorted by these characters instead of the time stamp. When submitting a list of input files, which is already sorted by time tamp, omitting the characters A and B xcube gen sorts the list internally and creates a wrong cube, first appending all input data with A and then with B.

Expected behavior
xcube gen should not sort again the input files. It should take the order given by the user.

[forman]

Generate S2-Plus data cubes for generic use case

[AliceBalfanz]

already implemented and merged into master. Can be used with parameter --sort when input data list should be sorted by xcube gen