Add serathius to etcd image owners

[serathius]

I would like to propose myself as an etcd image owner. Existing owner (jpbetz@) is no longer actively working on etcd, nor reviewing PR for etcd upgrade in K8s. Without active owner for etcd image, all reviews are need to be done by top level approvers.

About my work on etcd:

• Proposed, and lead release of etcd v3.5.0 to Kubernetes Update etcd to v3.5.0 #102294
• Heavily involved in Etcd v3.5.1 and v3.5.2 release, on both Etcd (Plans for v3.5.2 release etcd-io/etcd#13518) and Kubernetes side ([etcd] Bump etcd client to 3.5.1 #106589 (comment))
• Etcd maintainer Add Marek as a project maintainer etcd-io/etcd#13652

I hope that by having active image owner we can have etcd releases in Kubernetes delivered earlier and more effectivly.

/kind cleanup

NONE

[serathius]

cc @ahrtr @dims @liggitt

[dims]

/approve
/lgtm

[serathius]

/retest

[fedebongio]

/cc @lavalamp @deads2k @jpbetz @sttts
/triage accepted

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/retest

[BenTheElder]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BenTheElder, dims, serathius

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