Create new objects method get_or_none() to avoid boilerplate try/except

[Sebastian Muthwill]

Problem statement
Currently one can retrieve a single object, besides other ways, via Model.objects.filter().first()or Model.objects.get()

Model.objects.get() however will raise a DoesNotExist exception if there is no result. This leads into the situation that one has to try/except the query to handle it properly.

In some cases it is only relevant to do something if an entry exist.

Proposed solution
Provide a new method django.db.models.query._BaseQuerySet.get_or_none() that returns an object if available and None if not.

[Simon Charette]

Please take a minute to search the bug tracker before requesting features ​as documented and referenced in the please read first section of the ticket creation page

Duplicate of #33384, #11352, #2659, all of which were wontfixed.