Add support for COMMAND GETKEYSANDFLAGS

[dvora-h]

Pull Request check-list

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• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

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Description of change

closes #1947

[codecov-commenter]

Codecov Report

Merging #2141 (48514b6) into master (cb91eed) will increase coverage by 0.00%.
The diff coverage is 62.50%.

@@           Coverage Diff           @@
##           master    #2141   +/-   ##
=======================================
  Coverage   92.45%   92.45%           
=======================================
  Files         104      104           
  Lines       24364    24393   +29     
=======================================
+ Hits        22526    22553   +27     
- Misses       1838     1840    +2     

Impacted Files	Coverage Δ
redis/commands/core.py	83.96% <50.00%> (-0.04%)	⬇️
tests/test_commands.py	94.26% <66.66%> (-0.06%)	⬇️
redis/asyncio/connection.py	84.72% <0.00%> (-0.12%)	⬇️
tests/test_search.py	99.19% <0.00%> (+0.01%)	⬆️
redis/commands/search/field.py	98.57% <0.00%> (+0.08%)	⬆️
tests/conftest.py	87.25% <0.00%> (+0.79%)	⬆️

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