Fix wrong result when executing bulk requests with and without pipeline

[gaobinlong]

Closes #60437 .

When executing bulk api, if one request has no ingest pipeline and others have ingest pipeline, then the response is not correct, that's because in IngestService#executeBulkRequest() method, the cursor i doesn't move to next if the request has no ingest pipeline.

The main changes are:

1. fix the bug in IngestService#executeBulkRequest().
2. add some unit tests.
3. add a yaml test.

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/Ingest)

[danhermann]

@gaobinlong, thanks for fixing this. I'll get it merged in for the next release.

[danhermann]

@elasticmachine ok to test

[danhermann]

@elasticmachine update branch

[danhermann]

@gaobinlong, after running the tests on this one, it appears that one of the new tests (https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+pull-request-bwc/6187/testReport/junit/org.elasticsearch.backwards/MixedClusterClientYamlTestSuiteIT/test__p0_bulk_90_pipeline_One_request_has_pipeline_and_another_not_/) is failing. Could you take a look at that one?

[gaobinlong]

@danhermann, maybe because we have not done the backport, so the new yaml test executes failed when there is a mixed cluster. I'm not clear about how to handle this situation, maybe we can remove the new yaml test and only execute the newly added unit test ?

[danhermann]

@gaobinlong, ah, right. I was not paying attention to the fact that it was a backwards compatibility test that failed. If you will add the following lines (including indentation) to the 90_pipeline.yml file right after "One request has pipeline and another not":

  - skip:
      version: " - 7.99.99"
      reason: "change after backporting"

That will skip the mixed cluster tests for now and then after I backport the change for earlier releases, I'll change that so that the mixed cluster tests include that for the appropriate releases.

[gaobinlong]

@danhermann, I have done that, and all checks have passed yet.

[danhermann]

@gaobinlong, great, thank you! I'll get this merged and backported.

[tvernum]

@danhermann I think we can remove backport pending now. Right?

[danhermann]

Finished the last backport to 7.x and removed "backport pending" label.