Changes

feat(pingcap/tidb,pd,tidbcloud/cloud-storage-engine): enable previously disabled real cluster tests for job pull_integration_realcluster_test_next_gen (#3908)

Several next-gen real cluster integration tests were commented out due
to failures or timeouts. This PR re-enables these tests as they are now
stable and passing for job pull_integration_realcluster_test_next_gen.
 - 'tests/realtikvtest/scripts/next-gen/run-tests.sh bazel_addindextest'
- 'tests/realtikvtest/scripts/next-gen/run-tests.sh
bazel_pipelineddmltest'

The test result as follows: 
- tidb: 

https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftidb%2Fpull_integration_realcluster_test_next_gen/detail/pull_integration_realcluster_test_next_gen/5944/pipeline/394/

- tidbcloud/cloud-storage-engine: 

https://do.pingcap.net/jenkins/blue/organizations/jenkins/tidbcloud%2Fcloud-storage-engine%2Fdedicated%2Fpull_integration_realcluster_test_next_gen/detail/pull_integration_realcluster_test_next_gen/274/pipeline/777/

- pd: 

https://do.pingcap.net/jenkins/blue/organizations/jenkins/tikv%2Fpd%2Fpull_integration_realcluster_test_next_gen/detail/pull_integration_realcluster_test_next_gen/88/pipeline/501/
 (commit: 2689300)