fix: add __init__.py to key_value

[bkyryliuk]

SUMMARY

Adds init.py file

error log:

state/commands/create.py", line 24, in <module>
    from superset.key_value.commands.create import CreateKeyValueCommand
ModuleNotFoundError: No module named 'superset.key_value'

TESTING INSTRUCTIONS

N/A

[codecov]

Codecov Report

Merging #17730 (92c8f45) into master (63d9693) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 92c8f45 differs from pull request most recent head 3db9e0a. Consider uploading reports for the commit 3db9e0a to get more accurate results

@@            Coverage Diff             @@
##           master   #17730      +/-   ##
==========================================
- Coverage   67.70%   67.65%   -0.05%     
==========================================
  Files        1602     1602              
  Lines       64151    64146       -5     
  Branches     6773     6773              
==========================================
- Hits        43434    43401      -33     
- Misses      18864    18892      +28     
  Partials     1853     1853              

Flag	Coverage Δ
hive	?
mysql	82.15% <100.00%> (?)
postgres	?
presto	82.07% <100.00%> (?)
python	82.41% <100.00%> (-0.10%)	⬇️
sqlite	81.88% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/dashboards/filter_state/commands/get.py	86.66% <100.00%> (ø)
superset/key_value/commands/get.py	85.71% <100.00%> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-85.19%)	⬇️
superset/sql_validators/postgres.py	50.00% <0.00%> (-50.00%)	⬇️
superset/db_engine_specs/hive.py	70.27% <0.00%> (-16.99%)	⬇️
superset/reports/commands/log_prune.py	85.71% <0.00%> (-3.58%)	⬇️
superset/commands/importers/v1/utils.py	89.13% <0.00%> (-2.18%)	⬇️
superset/db_engine_specs/postgres.py	96.36% <0.00%> (-0.91%)	⬇️
superset/common/query_object.py	95.08% <0.00%> (-0.55%)	⬇️
superset/views/base_api.py	97.89% <0.00%> (-0.43%)	⬇️
... and 8 more

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[villebro]

LGTM