Changes

chore(prow-jobs/tikv/pd): enable auto runs for job pull_integration_realcluster_test_next_gen (#3883)

Let's enable auto runs for job
`pull_integration_realcluster_test_next_gen` to evaluate the stability,
but:
- keep it hidden on status report on pull requests
- set it as optional, so it will not block pull request merging.
 (commit: 6835168)