Add ability to kubectl argo rollouts set image *=myrepo/myimage

[jessesuen]

Adds the following capability:

$ kubectl argo rollouts set image rollout-baseline-vs-canary "*=argoproj/rollouts-demo:purple"
rollout "rollout-baseline-vs-canary" image updated

This matches the behavior of kubectl set image, e.g.:

kubectl set image daemonset abc *=nginx:1.9.1

[codecov]

Codecov Report

Merging #290 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #290   +/-   ##
=======================================
  Coverage   83.77%   83.77%           
=======================================
  Files          63       63           
  Lines        5665     5665           
=======================================
  Hits         4746     4746           
  Misses        671      671           
  Partials      248      248

Impacted Files	Coverage Δ
pkg/kubectl-argo-rollouts/cmd/set/set_image.go	100% <100%> (ø)	⬆️

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[dthomson25]

LGTM