Extended "CLUSTER NODES" parser to support special slot entries

[barshaul]

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Description of change

Extended "CLUSTER NODES" parser to support special slot entries (importing, migrating).
The returned dictionary will also contain another field called 'migrations' that will hold slots that are in migration process.
See https://redis.io/commands/cluster-nodes/#special-slot-entries for more info.

For example, for the following cluster:

49962d9126b7e587c7c93e9899df075055846123 127.0.0.1:16381@26381 master - 0 1648980066000 3 connected 10923-16383
bcded50bc75187199679b0cc7380b3240724b834 127.0.0.1:16379@26379 myself,master - 0 1648980062000 1 connected 0-5460 [1->-a0bb8017ee950c73510741f866f5ebf2aebc5662]
a0bb8017ee950c73510741f866f5ebf2aebc5662 127.0.0.1:16380@26380 master - 0 1648980065000 2 connected 5461-10922

the returned entry for node 16379 is:

print(r.cluster_nodes().get("127.0.0.1:16379"))
{'node_id': 'bcded50bc75187199679b0cc7380b3240724b834', 
'flags': 'myself,master', 
'master_id': '-', 
'last_ping_sent': '0', 
'last_pong_rcvd': '1648980178000', 
'epoch': '1',
 'slots': [['0', '5460']],
 'migrations': [{'slot': '1', 'node_id': 'a0bb8017ee950c73510741f866f5ebf2aebc5662', 'state': 'migrating'}],
 'connected': True}

[codecov-commenter]

Codecov Report

Merging #2080 (6a418f1) into master (143107a) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2080      +/-   ##
==========================================
+ Coverage   91.18%   91.19%   +0.01%     
==========================================
  Files         100      100              
  Lines       21456    21485      +29     
==========================================
+ Hits        19564    19593      +29     
  Misses       1892     1892              

Impacted Files	Coverage Δ
redis/client.py	89.46% <100.00%> (+0.16%)	⬆️
tests/test_cluster.py	97.36% <100.00%> (-0.10%)	⬇️
redis/asyncio/connection.py	82.52% <0.00%> (+0.11%)	⬆️
redis/asyncio/client.py	90.63% <0.00%> (+0.17%)	⬆️

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[dvora-h]

Thanks for that!