validate: provide likely reasons for typical validation errors

E.g., as reported on slack, there was a bunch of
```
TimeSeries/data (processing/spikes/Sweep_27): argument missing
```
validation errors. Thanks to the feedback from @rly on nwb slack channel:

from the path, i guess that the user wishes to store spike times in a TimeSeries. the most straightforward way to do that right now is to put the spike times in the timestamps array, but the data array is still required. here, until we implement a proper Events type (see https://github.com/NeurodataWithoutBorders/nwb-schema/issues/301), i recommend the user create a dummy array data consisting of ones for every value in the timestamps array.

Which gave me an idea that we might want to post-process some of the pynwb validation errors and provide guesses on what could have lead to them and how to mitigate.