Changed dynamic_startup_nodes default value to 'True'

[barshaul]

Pull Request check-list

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Description of change

Changed dynamic_startup_nodes default value to 'True' to prevent breaking backward compatibility

[codecov-commenter]

Codecov Report

Merging #2251 (835e65d) into master (63cf7ec) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2251      +/-   ##
==========================================
- Coverage   91.87%   91.82%   -0.05%     
==========================================
  Files         108      108              
  Lines       27786    27786              
==========================================
- Hits        25528    25515      -13     
- Misses       2258     2271      +13     

Impacted Files	Coverage Δ
redis/cluster.py	90.33% <ø> (ø)
tests/test_asyncio/test_cluster.py	97.09% <0.00%> (-0.49%)	⬇️
tests/test_cluster.py	96.85% <0.00%> (-0.24%)	⬇️
redis/asyncio/connection.py	83.84% <0.00%> (-0.23%)	⬇️
tests/test_graph.py	90.65% <0.00%> (-0.04%)	⬇️
tests/test_timeseries.py	100.00% <0.00%> (ø)
tests/conftest.py	86.50% <0.00%> (+0.05%)	⬆️

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