Add alpha command group

[martinmaly]

No description provided.

[yuwenma]

/lgtm

Is this alpha command aimed to manage the release stages like gcloud alpha/beta, whose sub-commands will be moved out of the alpha list once mature? I'm wondering if the maintenance cost would be a concern for kpt since our scenarios are much simpler than gcloud. @martinmaly Would it be sufficient to add the "alpha" to command descriptions (or further, give warnings when users run the alpha command) and not introduce the new 'alpha' group? This can reduce the further migration (and backport) work.

[martinmaly]

We probably could just add alpha descriptions. We need some place to quickly iterate on CLI UX related to porch, which is going to change rapidly. If there is exiting way to achieve this within kpt, happy to use it instead.

[droot]

/lgtm

Is this alpha command aimed to manage the release stages like gcloud alpha/beta, whose sub-commands will be moved out of the alpha list once mature? I'm wondering if the maintenance cost would be a concern for kpt since our scenarios are much simpler than gcloud. @martinmaly Would it be sufficient to add the "alpha" to command descriptions (or further, give warnings when users run the alpha command) and not introduce the new 'alpha' group? This can reduce the further migration (and backport) work.

For new commands, having them under alpha group is a good practice because it communicates the maturity of the command very explicitly. The harder part is to test new behavior for existing commands, there introducing a new flag (or environment feature flag) and marking it experimental is probably the only way to go.