Support for password-encrypted SSL private keys

[chayim]

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?
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Description of change

closes #1767
closes #1757

[codecov-commenter]

Codecov Report

Merging #1782 (59c44cc) into master (f82ab33) will increase coverage by 0.09%.
The diff coverage is 95.45%.

@@            Coverage Diff             @@
##           master    #1782      +/-   ##
==========================================
+ Coverage   94.22%   94.31%   +0.09%     
==========================================
  Files          74       75       +1     
  Lines       15681    15721      +40     
==========================================
+ Hits        14776    14828      +52     
+ Misses        905      893      -12     

Impacted Files	Coverage Δ
redis/client.py	89.96% <ø> (+0.11%)	⬆️
tests/conftest.py	91.13% <66.66%> (-0.75%)	⬇️
redis/connection.py	88.51% <100.00%> (+1.19%)	⬆️
tests/test_ssl.py	100.00% <100.00%> (ø)
tests/test_cluster.py	98.79% <0.00%> (+0.12%)	⬆️
redis/utils.py	90.32% <0.00%> (+6.45%)	⬆️

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