bash/zsh auto completion for clusterctl

[superbrothers]

User Story

As a developer/user/operator, I would like to use bash/zsh auto completion for clusterctl for improving work efficiency.

Detailed Description

I'd like to use bash/zsh auto completion for clusterctl command, like kubectl completion command.

$ source <(clusterctl completion bash)

I believe this will improve the experience for everyone - developers/users/operators.

Anything else you would like to add:

None

/kind feature

[superbrothers]

Auto completion of the kubectl command is provided by spf13/cobra library, and clusterctl also uses that library, so it can be provided easily.

I propose offering features in the next step:

1. Providing auto completion for subcommands and flags
   • Implementation of clusterctl completion bash/zsh command
2. Providing dynamic auto completion for cluster-api objects
   • Such as cluster object name completion for clusterctl get kubeconfig command

If you like this feature, I'll try to implement it.

[fabriziopandini]

Personally I'm +1 for 1 as a first step

[superbrothers]

/assign

[vincepri]

/milestone v0.4.0

Setting v0.4 as milestone for now, if it's a small enough change we can definitely backport this given that it could be useful

[wfernandes]

/area clusterctl