Adding `copy_store` convenience method for `Group`

[melonora]

[Description of PR] This PR adds a convenience method for copying the store of a Group to a destination store.

TODO:

• [x] Add unit tests and/or doctests in docstrings
• [x] Add docstrings and API docs for any new/modified user-facing classes and functions
• [x] New/modified features documented in docs/user-guide/*.md
• [x] Changes documented as a new file in changes/
• [x] GitHub Actions have all passed
• [x] Test coverage is 100% (Codecov passes)

@d-v-b

[codecov[bot]]

Codecov Report

:x: Patch coverage is 88.88889% with 3 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 60.97%. Comparing base (65fec71) to head (3e92ee9).

Files with missing lines	Patch %	Lines
src/zarr/core/group.py	88.88%	3 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3612      +/-   ##
==========================================
+ Coverage   60.90%   60.97%   +0.07%     
==========================================
  Files          86       86              
  Lines       10174    10199      +25     
==========================================
+ Hits         6196     6219      +23     
- Misses       3978     3980       +2     

Files with missing lines	Coverage Δ
src/zarr/testing/strategies.py	97.83% <ø> (ø)
src/zarr/core/group.py	70.85% <88.88%> (+0.57%)	:arrow_up:

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[melonora]

@d-v-b I know right now this won't work when zarr v2 is used. I can add that functionality as well or we say the convenience function is not supported for zarr v2.

[melonora]

added zarr v2 support. If in general the code is approved, I will add documentation.

[melonora]

@d-v-b @joshmoore I think I have now addressed all comments and I also added documentation, so I think this would be ready for a final round of review. @d-v-b thanks for your patience.

[melonora]

@d-v-b @joshmoore , just bumping in case you have some time to see whether you approve the current state:)

[melonora]

@d-v-b When the last test passes and if you are happy with the code changes I think this is good to go. Thanks for reviewing!