Add etcd release team

[jmhbnz]

We (sig-etcd leads) are creating a new GitHub team within our etcd-io org for the release team.

The members of this team will act as leads or advisors for upcoming etcd releases, on an agreed rotation and have repository write permissions to carry out etcd-io/etcd releases.

Historically etcd releases have only been carried out by maintainers which is challenging due to our currently small number of project maintainers. We've been gradually making improvements over time to address this, through improving our release processes, introducing release shadow roles and rotating the release manager for each release.

We now think the time is right to extend the release team beyond maintainers, to also include reviewers, as reviewers are all future maintainers for etcd that we have a lot of trust and confidence in.

cc @wenjiaswe, @ahrtr, @serathius

[jmhbnz]

We can easily bump this when a release is planned as sig-etcd-leads are OWNERS to /lgtm /approve a pr from a reviewer to bump it for the release then it can be reverted to bau afterward.

This ensures principle of least privileges is maintained.

[ahrtr]

/lgtm
/approve

/hold

Thanks @jmhbnz for driving this. Please feel free to un-hold after other maintainers reviewed this PR.

[wenjiaswe]

/lgtm
/approve

Thank you! @jmhbnz

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, jmhbnz, wenjiaswe

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Needs approval from an approver in each of these files:

• config/etcd-io/sig-etcd/OWNERS [ahrtr,jmhbnz,wenjiaswe]

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[jmhbnz]

Unholding after three business weeks for lazy consensus
/unhold