move starter manifests from test-infra to this repo and update docs

[tsj-30]

This commit moves the starter Prow configurations (S3, GCS, Azure) from
kubernetes/test-infra into kubernetes-sigs/prow under
config/prow/cluster/starter/.

All references in the getting-started deployment docs have been updated to
point to the new paths, and tackle’s defaultStarter URL now uses the
raw.githubusercontent.com path for the in-repo starter-gcs.yaml.

Fixes: #283

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: tsj-30
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[k8s-ci-robot]

Hi @tsj-30. Thanks for your PR.

I'm waiting for a github.com 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.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[Amulyam24]

/ok-to-test

[tsj-30]

CC: @petr-muller

[petr-muller]

/cc