Renames golang field names for blueGreen/canary to eliminate two API violations

[jessesuen]

Fixes two API violations since the golang field names did not match the API spec. I think it's too late to remove the HPAReplicas violation. The json field name should have been hpaReplicas and not HPAReplicas.

[codecov]

Codecov Report

Merging #206 into master will not change coverage.
The diff coverage is 95.29%.

@@           Coverage Diff           @@
##           master     #206   +/-   ##
=======================================
  Coverage   84.33%   84.33%           
=======================================
  Files          47       47           
  Lines        3945     3945           
=======================================
  Hits         3327     3327           
  Misses        441      441           
  Partials      177      177

Impacted Files	Coverage Δ
rollout/sync.go	77.83% <100%> (ø)	⬆️
utils/replicaset/canary.go	67.91% <100%> (ø)	⬆️
pkg/kubectl-argo-rollouts/cmd/list/rollloutinfo.go	90% <100%> (ø)	⬆️
rollout/canary.go	85.89% <100%> (ø)	⬆️
rollout/pause.go	96.36% <100%> (ø)	⬆️
rollout/analysis.go	82.96% <100%> (ø)	⬆️
rollout/controller.go	70% <100%> (ø)	⬆️
utils/defaults/defaults.go	100% <100%> (ø)	⬆️
rollout/service.go	91.48% <100%> (ø)	⬆️
utils/service/service.go	100% <100%> (ø)	⬆️
... and 5 more

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[dthomson25]

LGTM