kubectl default container behavior

[mengjiao-liu]

What type of PR is this?

/kind feature

What this PR does / why we need it:

specify the default container for kubectl attach, cp, exec command with annotation kubectl.kubernetes.io/default-container
The following files are created
staging/src/k8s.io/kubectl/pkg/cmd/util/default-container.go
This avoids duplicate code and help having a single place for maintenance.

more details can be seen in the KEP KEP-2227: default container behavior

Which issue(s) this PR fixes:

Ref enhancements issue

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Users might specify the `kubectl.kubernetes.io/default-container` annotation in a Pod to preselect container for kubectl commands.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

- [KEP] https://github.com/kubernetes/enhancements/blob/master/keps/sig-cli/2227-kubectl-default-container/README.md

[k8s-ci-robot]

Hi @mengjiao-liu. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[dougsland]

On queue for the review.
/cc @pacoxu

[pacoxu]

/lgtm
👍

[pacoxu]

/ok-to-test

[dougsland]

@mengjiao-liu looks like there is a conflict. Could you please rebase so we can do a fresh review?

[dougsland]

/cc @eddiezane

[pacoxu]

/lgtm
@dougsland

[dougsland]

/lgtm
Thanks @mengjiao-liu @pacoxu

[annajung]

Hi @mengjiao-liu, a friendly reminder that the code freeze for 1.21 is today.
Please make sure to get the necessary approval for this to merge by EOD PST.

[dougsland]

/lgtm

[eddiezane]

/retest
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: eddiezane, mengjiao-liu, pacoxu

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• staging/src/k8s.io/kubectl/OWNERS [eddiezane]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[palnabarun]

Adding the PR to the v1.21 milestone, since most of the changes were lgtm'ed prior to Code Freeze and the change here doesn't carry much risk.

/milestone v1.21

[pacoxu]

/retest