Add gce_init.sh startup script and revise instructions

[johnbelamaric]

Added a startup script, so the user can launch Nephio Sandbox in a single gcloud command.

[johnbelamaric]

cc @electrocucaracha @vjayaramrh @radoslawc

The actual command won't work until the PR merges, because it tries to pull the script from GitHub. If you want to try it, then pull out the PR and run it using gcloud compute instances create --machine-type e2-standard-8 --boot-disk-size 200GB --image-family=ubuntu-2204-lts --image-project=ubuntu-os-cloud --metadata-from-file=startup-script=./gce_init.sh nephio-r1-e2e.

[vjayaramrh]

cc @electrocucaracha @vjayaramrh @radoslawc

The actual command won't work until the PR merges, because it tries to pull the script from GitHub. If you want to try it, then pull out the PR and run it using gcloud compute instances create --machine-type e2-standard-8 --boot-disk-size 200GB --image-family=ubuntu-2204-lts --image-project=ubuntu-os-cloud --metadata-from-file=startup-script=./gce_init.sh nephio-r1-e2e.

@johnbelamaric Will review

[nephio-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: johnbelamaric, vjayaramrh
Once this PR has been reviewed and has the lgtm label, please assign radoslawc for approval by writing /assign @radoslawc in a comment. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

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

[johnbelamaric]

Closing in favor of #56.