fix: ping instead of checking pod readiness

[com6056]

Description

Right now, since the operator relies on checking pod readiness, it makes using a more robust readiness probe not possible. This changes it so instead of checking the pod readiness, we just directly PING all of the redis nodes instead (which the default readiness probe does anyways).

Also exposes podManagementPolicy to be configurable since you need Parallel if you are using readiness probes that check cluster health.

Fixes #1016

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Tests have been added/modified and all tests pass.
• Functionality/bugs have been confirmed to be unchanged or fixed.
• I have performed a self-review of my own code.
• Documentation has been updated or added where necessary.

Additional Context

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 25 lines in your changes missing coverage. Please review.

Project coverage is 45.97%. Comparing base (d121d86) to head (ae15bc7).
Report is 91 commits behind head on master.

Files	Patch %	Lines
k8sutils/cluster-scaling.go	0.00%	16 Missing ⚠️
k8sutils/statefulset.go	42.85%	8 Missing ⚠️
controllers/rediscluster_controller.go	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1038       +/-   ##
===========================================
+ Coverage   35.20%   45.97%   +10.76%     
===========================================
  Files          19       20        +1     
  Lines        3213     2730      -483     
===========================================
+ Hits         1131     1255      +124     
+ Misses       2015     1400      -615     
- Partials       67       75        +8     

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[drivebyer]

@com6056 Could you please resolve the conflict