Make dashboard replicas configurable

[kylehodgetts]

Currently, only 1 dashboard instance is configured to run when the cluster is spun up.
This requires a manual edit of the kubernetes-dashboard deployment to change this.

If a cluster goes through an update, then the figure is then reset back to one.

This change allows for the value to be configured.

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #1539 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1539      +/-   ##
==========================================
- Coverage   25.46%   25.45%   -0.01%     
==========================================
  Files          97       97              
  Lines        5003     5004       +1     
==========================================
  Hits         1274     1274              
- Misses       3582     3583       +1     
  Partials      147      147

Impacted Files	Coverage Δ
pkg/api/cluster.go	0% <0%> (ø)	⬆️

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