Adding support for non-decodable commands

[chayim]

Some commands (i.e DUMP) should never have their response decoded, as they return binaries, not encoded blobs

fixes #1254
closes #1732

[codecov-commenter]

Codecov Report

Merging #1731 (1448a65) into master (d2b2333) will increase coverage by 0.00%.
The diff coverage is 87.50%.

@@           Coverage Diff           @@
##           master    #1731   +/-   ##
=======================================
  Coverage   89.04%   89.04%           
=======================================
  Files          53       53           
  Lines       11052    11058    +6     
=======================================
+ Hits         9841     9847    +6     
  Misses       1211     1211           

Impacted Files	Coverage Δ
redis/connection.py	71.11% <66.66%> (ø)
redis/client.py	82.15% <100.00%> (+0.06%)	⬆️
redis/commands/core.py	83.91% <100.00%> (+0.03%)	⬆️
redis/sentinel.py	86.53% <100.00%> (ø)

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