feat: generate k8s client only once

[MathieuCesbron]

Description

I realised that we create a new k8s client every time we need it. It's quite consuming, we should create it at the start of the controller and use it for his lifetime. We then pass the client down to each functions.

I realised this because we cannot add integration tests with EnvTest if we create a new client every time we need one #748

PS: It looks like the coverage test fail because some code removed was tested so it technically lowers the coverage.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• Functionality/bugs have been confirmed to be unchanged or fixed.
• I have performed a self-review of my own code.

[codecov]

Codecov Report

Attention: 110 lines in your changes are missing coverage. Please review.

Comparison is base (e57531a) 28.80% compared to head (aa7042b) 29.25%.

Files	Patch %	Lines
k8sutils/poddisruption.go	0.00%	22 Missing ⚠️
k8sutils/redis-cluster.go	5.00%	19 Missing ⚠️
k8sutils/statefulset.go	0.00%	16 Missing ⚠️
k8sutils/services.go	0.00%	12 Missing ⚠️
k8sutils/redis-sentinel.go	0.00%	10 Missing ⚠️
controllers/rediscluster_controller.go	0.00%	8 Missing ⚠️
k8sutils/redis-replication.go	0.00%	6 Missing ⚠️
k8sutils/redis-standalone.go	0.00%	6 Missing ⚠️
controllers/redisreplication_controller.go	0.00%	3 Missing ⚠️
controllers/redissentinel_controller.go	0.00%	3 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #750      +/-   ##
==========================================
+ Coverage   28.80%   29.25%   +0.44%     
==========================================
  Files          19       19              
  Lines        3291     3241      -50     
==========================================
  Hits          948      948              
+ Misses       2308     2258      -50     
  Partials       35       35              

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[drivebyer]

lgtm