Return error dictionary for COCOValidator().validate_dataset()

[andreap-bh]

Is your feature request related to a problem? Please describe.
The feature is not related to a problem, but it's a missing capability which could be useful to have. In practice, when the method COCOValidator().validate_dataset() fails some checks, it only prints an error message to screen, but it doesn't return the dictionary with the failed checks. Example error message:

return super(COCODataFrame, self).set_index(keys, drop, append, inplace, verify_integrity)
ERROR:root: -- Error for data having id:  0. Missing mandatory key supercategory.
ERROR:root: | Test failed: this is not a valid COCO dataset: There are missing mandatory keys in the COCO categories.
Verify if this dataset is in valid COCO format: False

Describe the solution you'd like
Return a dictionary with failed checks, so that callee can do something with it. For example, it could save a list of the failed checks to disc, or it could try to fix some of them.

Describe alternatives you've considered
N/A

Additional context
N/A

[andreap-bh]

@valvgab-bh issue description improved as asked by you