deprecate(stores): add deprecation warnings to stores that we plan to remove in v3

[jhamman]

This adds a simple deprecation warning to the following stores:

• [x] DBMStore
• [x] LMDBStore
• [x] SQLiteStore
• [x] MongoDBStore
• [x] RedisStore
• [x] ABSStore
• [x] NestedDirectoryStore (note: this was already just a special case of the Directory store for v2

closes https://github.com/zarr-developers/zarr-python/issues/1756

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
• [ ] New/modified features documented in docs/tutorial.rst
• [x] Changes documented in docs/release.rst
• [x] GitHub Actions have all passed
• [x] Test coverage is 100% (Codecov passes)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.98%. Comparing base (9d046ea) to head (f500c51).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1801   +/-   ##
=======================================
  Coverage   99.98%   99.98%           
=======================================
  Files          38       38           
  Lines       14659    14667    +8     
=======================================
+ Hits        14657    14665    +8     
  Misses          2        2           

Files	Coverage Δ
zarr/_storage/absstore.py	100.00% <100.00%> (ø)
zarr/_storage/store.py	100.00% <100.00%> (ø)
zarr/storage.py	100.00% <100.00%> (ø)

[jhamman]

@zarr-developers/python-core-devs - this is ready for a review. @d-v-b is out of town this week otherwise I'd be hounding him!