network annotation to hold egress NAT gateway IP

[vasu-dasari]

NetworkGatewayIPAnnotationKey is the network annotation key used to hold egress NAT gateway IP.

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[google-oss-prow[bot]]

Hi @vasu-dasari. Thanks for your PR.

I'm waiting for a GoogleCloudPlatform 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](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.

[shouri007]

/ok-to-test

[shouri007]

/approved /lgtm

[shouri007]

/lgtm /approve

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shouri007, vasu-dasari

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](https://github.com/GoogleCloudPlatform/gke-networking-api/blob/main/OWNERS)~~ [shouri007] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[liuyuan10]

@vasu-dasari I wonder why this annotation needs to to here. apis/network is for multinetwork and this annotation is for gdch. I don't even see it needs to be open sourced.