Support Elasticsearch v9 (for v10.11) (#35925)

* Support Elasticsearch v9 alongside v8

* Add CI workflow changes for Elasticsearch v8/v9 testing

* Support Elasticsearch v7 in addition to v8/v9, add v7 CI test job

Lowers the minimum supported ES version from 8 to 7 to avoid dropping
v7 support in a dot release. Adds a dedicated CI job to verify v7
compatibility alongside the existing v8 and v9 (default) jobs.

* Fix ES7 plugin install crash on cgroup v2 hosts

* Fix ES 7 container startup on cgroup v2 Linux (GitHub Actions)

ES 7 bundles JDK 11, which crashes with a NullPointerException in
CgroupV2Subsystem.getMountPoint() on modern Linux kernels that use
cgroup v2 (including GitHub Actions ubuntu-latest runners). The flag
was already set during the Dockerfile RUN step, but not at runtime.

Adding -XX:-UseContainerSupport to ES_JAVA_OPTS in docker-compose
fixes the crash. The flag is harmless on ES 8/9 which ship JDK 17+
where the cgroup v2 bug is fixed (it simply opts out of container-aware
JVM sizing).

* Capture docker compose logs in CI test artifact

* Use ES 7.17.29 for v7 CI test; remove cgroup v2 workarounds

ES 7.17.0 bundled JDK 17.0.1 which had a cgroup v2 bug
(CgroupV2Subsystem NPE) not fixable via -XX:-UseContainerSupport.
ES 7.17.29 bundles JDK 22 where the bug is long fixed.

Reverts the -XX:-UseContainerSupport workarounds added in the
previous two commits as they were based on a wrong diagnosis
and are no longer needed.

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

.github/workflows/server-ci-template.yml

@@ -264,6 +264,30 @@ jobs:
       datasource: mmuser:mostest@tcp(mysql:3306)/mattermost_test?charset=utf8mb4&multiStatements=true&maxAllowedPacket=4194304
       drivername: mysql
       logsartifact: mysql-server-test-logs
+  test-elasticsearch-v8:
+    name: Elasticsearch v8 Compatibility
+    needs: check-mattermost-vet
+    uses: ./.github/workflows/server-test-template.yml
+    secrets: inherit
+    with:
+      name: Elasticsearch v8 Compatibility
+      datasource: postgres://mmuser:mostest@postgres:5432/mattermost_test?sslmode=disable&connect_timeout=10
+      drivername: postgres
+      logsartifact: elasticsearch-v8-server-test-logs
+      elasticsearch-version: "8.9.0"
+      test-target: "test-server-elasticsearch"
+  test-elasticsearch-v7:
+    name: Elasticsearch v7 Compatibility
+    needs: check-mattermost-vet
+    uses: ./.github/workflows/server-test-template.yml
+    secrets: inherit
+    with:
+      name: Elasticsearch v7 Compatibility
+      datasource: postgres://mmuser:mostest@postgres:5432/mattermost_test?sslmode=disable&connect_timeout=10
+      drivername: postgres
+      logsartifact: elasticsearch-v7-server-test-logs
+      elasticsearch-version: "7.17.29"
+      test-target: "test-server-elasticsearch"
   test-coverage:
     # Skip coverage generation for cherry-pick PRs into release branches.
     if: ${{ github.event_name != 'pull_request' || !startsWith(github.event.pull_request.base.ref, 'release-') }}