Configurable heartbeat value for WsApiClient

[GlassOfWhiskey]

Thir PR adds a configurable heartbeat value to the WsApiClient constructor, which defaults to None. This prevents connection timeouts when executing long commands with no outputs on remote pods.
A unit test has also been added to check that the heartbeat argument is correctly received in the constructor.

Fixes #193

[codecov]

Codecov Report

Merging #195 (2ec63be) into master (aa44bfa) will increase coverage by 0.01%.
The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
+ Coverage   27.42%   27.43%   +0.01%     
==========================================
  Files         702      702              
  Lines       93764    93779      +15     
==========================================
+ Hits        25712    25727      +15     
  Misses      68052    68052              

Impacted Files	Coverage Δ
kubernetes_asyncio/stream/ws_client.py	91.52% <80.00%> (+0.45%)	⬆️
kubernetes_asyncio/stream/ws_client_test.py	95.91% <100.00%> (+1.32%)	⬆️

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[tomplus]

Many thanks!

[tomplus]

Released in v22.6.3.