release-notes check subcommand

[puerco]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR adds a new check subcommand to release-notes. This command is designed tu run in CI to make it easy to enforce kubernetes-style release notes in PRs. The subcommand takes one or more PR numbers and will exit non-zero if the PRs are missing the release-notes block or a valid release note. It supports NONE or adding the release-note-none label to skip the note enforcement.

Here's the output from the subcommand help:

$] release-notes check  --help

release-notes check checks one or more PRs to ensure they contain
a valid release note. It is a subcommand designed to run in a postsubmit job to
block PRs missing a release note.

release-notes check will retrieve pull request data using the GitHub API and
look for a valid release notes block in the PR body. For example:

```release-note
Fixed a bug to make my software even more awesome
`` `

When enforcing release notes in PRs, we recommend adding the release-notes block
to your PR templates. See how Kubernetes does it here:
https://github.com/kubernetes/release/blob/d546da8a2ec580ea4c024637234cc976a6ba398a/.github/PULL_REQUEST_TEMPLATE.md?plain=1#L45-L57

If you want to skip the release notes check, you can create a new "release-notes-none"
label to your PR or type "NONE" in the notes block:

```release-note
NONE
`` `

Either of these will instruct the release note checked to allow a PR without a
valid note.

To generate release notes from these blocks, use release-notes generate.

Usage:
  release-notes check [flags]

Flags:
      --debug                    Enable debug logging
      --github-base-url string   Base URL of github
  -h, --help                     help for check
      --org string               Name of github organization (default "kubernetes")
      --pr ints                  pull request number(s) to check
      --repo string              Name of github repository (default "kubernetes")

When failing the subcommand will print a short help text to guide contributors looking at the logs:

release-notes check --pr=3403 --repo=release 

Error Checking Release Notes:

The pull request(s) specified do not have a valid release note.

Make sure the PRs have a ```release-note block (see help) in the PR body with markdown text
clearly specifying the change being introduced in your commits.

If you want to skip the release notes check, you can type NONE in the release notes block
or add a "release-notes-none" (without quotes) to your PR. This will
tell the release notes checker to allow PRs without a note.

For more information see:
https://github.com/kubernetes/release/tree/master/cmd/release-notes

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

This subcommand will be part of a new release-notes action in k-sigs/release-actions 🚀
(first part is here)

/assign @cpanato

Does this PR introduce a user-facing change?

The `release-notes` utility will now have subcommands to support more functionality
- The original functionality of `release-notes` has now been moved to the `release-notes generate` subcommand. This is the default subcommand to avoid breaking compatibility.
- We now have a new `release-notes check` subcommand to verify if PRs have a valid release note

Signed-off-by: Adolfo García Veytia (Puerco) adolfo.garcia@uservers.net

[cpanato]

Cool nice one

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, puerco

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Needs approval from an approver in each of these files:

• cmd/release-notes/OWNERS [cpanato,puerco]
• pkg/notes/OWNERS [cpanato,puerco]

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