Add supports_groups=True to Zarr backend

[sjperkins]

• Closes Zarr backend isn't configured with supports_groups=True #10808
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

[sjperkins]

Any advice for the permission denied error on Windows? The new test case doesn't look significantly different from those above it?

[shoyer]

Any advice for the permission denied error on Windows? The new test case doesn't look significantly different from those above it?

This usually means that we didn't remember close a file.

But honestly Windows is super picky, and I have struggled to track these down in many cases.

Feel free to xfail this test on Windows. Here's an example of how to do that:

xarray/xarray/tests/test_backends.py

Lines 7539 to 7542 in eed12c4

	@pytest.mark.xfail(
	ON_WINDOWS,
	reason="Permission errors from Zarr: https://github.com/pydata/xarray/pull/10793",
	)

[sjperkins]

rtd build failure appears unrelated: due to a http timeout

[shoyer]

Thanks @sjperkins !

It looks like the docs build is failing because docs.scipy.org is not supporting HTTPS currently

[sjperkins]

Thanks for the review and merge @shoyer.