docs for migration to apiVersion networking.k8s.io v1

[longwuyuan]

What this PR does / why we need it:

• This PR introduces some documentation related to migration to K8s v1.22
• All beta version of the ingress api are deprecated in K8s v1.22
• Some backward compatibility will break
• Some usage specifications will break
• The documentation introduced here will improve subsequently

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Which issue/s this PR fixes

fixes ##7397

How Has This Been Tested?

Tested locally on a kind cluster

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[k8s-ci-robot]

@longwuyuan: This issue is currently awaiting triage.

If Ingress contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

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.

[rikatz]

Overall it looks good

Just some minor changes!

Thanks

[rikatz]

/lgtm
/approve
Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: longwuyuan, rikatz

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:

• OWNERS [rikatz]

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