Add support for CLUSTER MYID

[enjoy-binbin]

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Description of change

add support for CLUSTER MYID, invoke cluster-tests passed

Closes #1972

[codecov-commenter]

Codecov Report

Merging #2063 (47c66e5) into master (ef4caf5) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2063      +/-   ##
==========================================
+ Coverage   91.20%   91.21%   +0.01%     
==========================================
  Files         100      100              
  Lines       21319    21325       +6     
==========================================
+ Hits        19443    19452       +9     
+ Misses       1876     1873       -3     

Impacted Files	Coverage Δ
redis/commands/cluster.py	93.57% <100.00%> (+0.09%)	⬆️
tests/test_cluster.py	97.54% <100.00%> (+0.12%)	⬆️
redis/asyncio/client.py	90.63% <0.00%> (+0.17%)	⬆️

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[dvora-h]

@enjoy-binbin Awesome! thanks for this.

[enjoy-binbin]

i also have a question, for a RedisClusterCommands command
when do we use target_nodes or target_node or nothing (a little confused)

[enjoy-binbin]

@dvora-h I suppose we should add a "CLUSTER MYID": str_if_bytes in AbstractRedis?
Currently it returns bytes, like b'bcb7b78f841d0b656517aa991b9806f293e2d575'