Support fish shell completion (#3231)

* Support fish shell completion

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

* Use spf13/cobra library to generate zsh completion

reference to https://github.com/spf13/cobra/blob/v1.1.1/shell_completions.md

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

* Update velero completion help message

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

* Add changelog

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

* Update cobra version in go.mod instead of replace

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

* Replace yourprogram to velero

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

changelogs/unreleased/3231-jenting

@@ -0,0 +1 @@
+Support fish shell completion

go.mod

@@ -3,7 +3,6 @@ module github.com/vmware-tanzu/velero
 go 1.15
 
 require (
-	cloud.google.com/go v0.46.2 // indirect
 	github.com/Azure/azure-sdk-for-go v42.0.0+incompatible
 	github.com/Azure/go-autorest/autorest v0.9.6
 	github.com/Azure/go-autorest/autorest/azure/auth v0.4.2
@@ -27,7 +26,7 @@ require (
 	github.com/robfig/cron v1.1.0
 	github.com/sirupsen/logrus v1.4.2
 	github.com/spf13/afero v1.2.2
-	github.com/spf13/cobra v0.0.7
+	github.com/spf13/cobra v1.1.1
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.4.0
 	golang.org/x/mod v0.1.0