Changes

hub registry: migrate tikv/migration pipeline images off hub.pingcap.net (#4327)

* Switches tikv/migration pod templates off `hub.pingcap.net` and onto
GHCR.
* Removes unused report sidecar from non-Kafka integration pod.

## Image updates

| Old (`hub.pingcap.net/jenkins/...`) | New / Action |
|---|---|
| `centos7_golang-1.21:latest` |
`ghcr.io/pingcap-qe/ci/jenkins:v2024.10.8-119-g4e56df7-go1.21` |
| `golang-tini:1.21` |
`ghcr.io/pingcap-qe/ci/jenkins:v2024.10.8-119-g4e56df7-go1.21` |
| `network-multitool` | `wbitt/network-multitool` (already public) |
| `python3-requests:latest` | container removed (unused) |

## Files changed
- `pipelines/tikv/migration/latest/pod-pull_integration_test.yaml` —
golang image -> `ci/jenkins`, drop report sidecar, keep net-tool/utils
public
- `pipelines/tikv/migration/latest/pod-pull_integration_kafka_test.yaml`
— golang image -> `ci/jenkins`, keep net-tool/utils public

`ghcr.io/pingcap-qe/ci/jenkins:...-go1.21` carries the same toolchain as
the prior base image but defaults to user `jenkins`, matching historical
UID/GID expectations in these jobs.

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>hub registry: migrate images for
tikv/migration</issue_title>
> <issue_description>Replace hub.pingcap.net image pulls/pushes for
tikv/migration with a cloud-accessible registry.
> 
> Acceptance criteria:
> - No hub.pingcap.net references in jobs/pipelines for tikv/migration
> - Image registry endpoints documented and validated
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes PingCAP-QE/ci#4227

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
Co-authored-by: wuhuizuo <wuhuizuo@126.com>
 (commit: d11da55)