Migrate remaining PR jobs to Buildkite #15444 (#15450)

This commit adds the remaining steps for the Buildkite pull request pipeline i.e.

- `IT Persistent Queues / part 1`
- `IT Persistent Queues / part 2`
- `x-pack unit tests`
- `x-pack integration`

Once merged we will be able to retire the corresponding Logstash pull request multijob.

Relates:

- https://github.com/elastic/logstash/pull/15438
- https://github.com/elastic/logstash/pull/15437
- https://github.com/elastic/ingest-dev/issues/1721
- https://github.com/elastic/logstash/pull/15279

(cherry picked from commit 555a8ff8e3)

Co-authored-by: Dimitrios Liappis <dimitrios.liappis@gmail.com>

.buildkite/pull_request_pipeline.yml

@@ -72,3 +72,65 @@ steps:
 
       source .buildkite/scripts/common/container-agent.sh
       ci/integration_tests.sh split 1
+
+  - label: ":lab_coat: IT Persistent Queues / part 1"
+    key: "integration-tests-qa-part-1"
+    agents:
+      image: "docker.elastic.co/ci-agent-images/platform-ingest/buildkite-agent-logstash-ci-no-root"
+      cpu: "8"
+      memory: "16Gi"
+      ephemeralStorage: "100Gi"
+      # Run as non root (logstash) user. UID is hardcoded in image.
+      imageUID: "1002"
+    command: |
+      set -euo pipefail
+
+      source .buildkite/scripts/common/container-agent.sh
+      export FEATURE_FLAG=persistent_queues
+      ci/integration_tests.sh split 0
+
+  - label: ":lab_coat: IT Persistent Queues / part 2"
+    key: "integration-tests-qa-part-2"
+    agents:
+      image: "docker.elastic.co/ci-agent-images/platform-ingest/buildkite-agent-logstash-ci-no-root"
+      cpu: "8"
+      memory: "16Gi"
+      ephemeralStorage: "100Gi"
+      # Run as non root (logstash) user. UID is hardcoded in image.
+      imageUID: "1002"
+    command: |
+      set -euo pipefail
+
+      source .buildkite/scripts/common/container-agent.sh
+      export FEATURE_FLAG=persistent_queues
+      ci/integration_tests.sh split 1
+
+  - label: ":lab_coat: x-pack unit tests"
+    key: "x-pack-unit-tests"
+    agents:
+      image: "docker.elastic.co/ci-agent-images/platform-ingest/buildkite-agent-logstash-ci-no-root"
+      cpu: "8"
+      memory: "16Gi"
+      ephemeralStorage: "100Gi"
+      # Run as non root (logstash) user. UID is hardcoded in image.
+      imageUID: "1002"
+    command: |
+      set -euo pipefail
+
+      source .buildkite/scripts/common/container-agent.sh
+      x-pack/ci/unit_tests.sh
+
+  - label: ":lab_coat: x-pack integration"
+    key: "integration-tests-x-pack"
+    agents:
+      image: "docker.elastic.co/ci-agent-images/platform-ingest/buildkite-agent-logstash-ci-no-root"
+      cpu: "8"
+      memory: "16Gi"
+      ephemeralStorage: "100Gi"
+      # Run as non root (logstash) user. UID is hardcoded in image.
+      imageUID: "1002"
+    command: |
+      set -euo pipefail
+
+      source .buildkite/scripts/common/container-agent.sh
+      x-pack/ci/integration_tests.sh