passing missing arguments when opening zarr, hdf5 and netcdft4 datatrees

[aladinor]

• Closes arguments not passed to open_groups_as_dict function when opening a datatree #9427
• User visible changes (including notable bug fixes) are documented in whats-new.rst

[TomNicholas]

@kmuehlbauer or @keewis would you mind just confirming that this is the correct way to handle these kwargs?

[kmuehlbauer]

@TomNicholas Yes, I think this is correct. I'm not sure if this can be restructured and would rely on @keewis expertise.

[keewis]

sorry for the delay, I've been far away from any computer for the past two weeks.

I'd say short of adding the arguments to **kwargs that's the only thing we can do, as really we're just forwarding to open_groups_as_dict (which by the way I thought we wanted to call just open_groups? Maybe I missed some discussion on that).

[keewis]

this should be pretty uncontroversial, so I'm merging this now. Thanks @aladinor