pytest `snapshot_folder_name` and `allow_multiple_equivalent_writes_to_one_location` about selfie

[nedtwigg]

We now have a SelfieSettings, but there are two parts missing:

selfie/python/pytest-selfie/pytest_selfie/SelfieSettingsAPI.py

Lines 15 to 23 in f1325e8

	@property
	def allow_multiple_equivalent_writes_to_one_location(self) -> bool:
	"""Allow multiple equivalent writes to one location."""
	return True
	@property
	def snapshot_folder_name(self) -> Optional[str]:
	"""Defaults to None, which means that snapshots are stored right next to the test that created them."""
	return None

Users should be able to set them like so:

selfie/python/pytest-selfie/pytest_selfie/SelfieSettingsAPI.py

Line 10 in f1325e8

"""API for configuring the selfie plugin, you can set its values like this https://docs.pytest.org/en/7.1.x/reference/customize.html#configuration-file-formats"""

Right now our docs say something like this:

If you want the disk snapshots to live in a different folder, set snapshotFolderName using

whatever we have to say there should be accurate