Add `__getattr__` at `arviz` module level for better error message when importing InferenceData

[OriolAbril]

It is possible to redefine the __getattr__ method of a module which we can use to check when the InferenceData attribute is being requested and error out with a message linking to the migration guide. Otherwise call the super unmodified method

[SpandanBhoiIITM]

Hi, I’m interested in working on this issue.

I’ve already set up ArviZ locally and run the test suite.
I would like to try implementing the module-level getattr for this.

Please let me know if I can work on it.

[OriolAbril]

sorry but this is not available @SpandanBhoiIITM, we'll most probably get to this later this week or the next one. See https://python.arviz.org/en/stable/contributing/contributing_prs.html#steps-before-starting-work for the usual workflows and conventions around distributing work