Changes

feat(tikv/pd): add PD real cluster integration test job for next-gen kernel (#3777)

This pull request introduces a new Jenkins-based integration test job
for the `tikv/pd` repository, specifically targeting the "Next Gen" real
cluster integration tests. It adds all necessary pipeline, pod template,
and Prow configuration files to support running these tests in a Jenkins
environment, alongside updates to cache key usage in a related TiDB
pipeline for consistency.

**New Jenkins Integration Test Job for tikv/pd:**

* Added a new Jenkins pipeline job definition for
`tikv/pd/pull_integration_realcluster_test_next_gen`, including job
parameters, SCM configuration, and log rotation
(`jobs/tikv/pd/latest/pull_integration_realcluster_test_next_gen.groovy`).
* Implemented the Jenkins pipeline script for the integration tests,
handling checkout, preparation (including binary downloads and caching),
and a matrix of test stages with reporting and artifact archiving
(`pipelines/tikv/pd/latest/pull_integration_realcluster_test_next_gen/pipeline.groovy`).
* Added Kubernetes pod templates for both the main build pod and the
test pod, specifying resource requirements, container images, volume
mounts, and node affinity (`main-pod.yaml`, `test-pod.yaml`).
[[1]](diffhunk://#diff-3425317e0ae8375e751ef6a78b53e3de1248e1a97100321e3cee04d3af5ec302R1-R35)
[[2]](diffhunk://#diff-075018e84467a3b3235ba17f792a7da60cc6e2615829f3b8242604433720b7bdR1-R92)

**Prow Job Configuration Updates:**

* Updated the Prow presubmit configuration to add the new Jenkins job,
using a Jenkins agent (not Kubernetes), and set it as optional and not
always run until stabilized
(`prow-jobs/tikv/pd/latest-presubmits-next-gen.yaml`).
* Refactored Prow job definitions to use YAML anchors for Jenkins and
Kubernetes job types, improving maintainability and clarity
(`prow-jobs/tikv/pd/latest-presubmits-next-gen.yaml`).
[[1]](diffhunk://#diff-0a1ed9e4783f485246ae8e0405d3d1559accdc9e203bb3363fc6d6d96419284eR16-L23)
[[2]](diffhunk://#diff-0a1ed9e4783f485246ae8e0405d3d1559accdc9e203bb3363fc6d6d96419284eL43-L46)

**Related Consistency Fix:**

* Updated the TiDB integration test pipeline to use the shared
`prow.getCacheKey` utility for cache keys, improving consistency and
cache hit rates
(`pipelines/pingcap/tidb/latest/pull_integration_realcluster_test_next_gen/pipeline.groovy`).

---------

Co-authored-by: Ti Chi Robot <ti-community-prow-bot@tidb.io>
 (commit: d16ad19)