Add --kube-context flag support to all helm-diff commands #902

Job	Run time
Build & Test	3m 20s
Integration Tests (v3.19.0-rc.1)	57s
Integration Tests (v3.18.6)	58s
helm install (ubuntu-latest, default, false, v3.18.6)	9s
helm install (macos-latest, default, false, v3.18.6)	11s
helm install (windows-latest, default, false, v3.19.0-rc.1)	28s
helm install (windows-latest, cygwin, false, v3.19.0-rc.1)	1m 46s
helm install (windows-latest, cygwin, false, v3.18.6)	1m 31s
helm install (macos-latest, default, false, v3.19.0-rc.1)	10s
helm install (windows-latest, default, false, v3.18.6)	1m 1s
helm install (windows-latest, wsl, false, v3.18.6)	1m 7s
helm install (windows-latest, wsl, false, v3.19.0-rc.1)	1m 10s
helm install (ubuntu-latest, sh, false, v3.19.0-rc.1, alpine)	11s
helm install (ubuntu-latest, sh, false, v3.18.6, alpine)	12s
helm install (ubuntu-latest, default, false, v3.19.0-rc.1)	10s
	13m 21s

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