feat: add shortened option -A for --all-namespaces

[sakajunquality]

kubectl's --all-namespaces has an shortened alias -A.
It would be nice if kubectl-argo-rollouts has the same alias.

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #615 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #615   +/-   ##
=======================================
  Coverage   85.71%   85.71%           
=======================================
  Files          87       87           
  Lines        8380     8380           
=======================================
  Hits         7183     7183           
  Misses        859      859           
  Partials      338      338           

Impacted Files	Coverage Δ
...kg/kubectl-argo-rollouts/cmd/list/list_rollouts.go	86.31% <100.00%> (ø)

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