… include

Switch from a trigger job to a GitLab CI include, pulling the PHP
Laravel Realworld parallel benchmark jobs directly into this pipeline.
Adds two new stages: php-laravel-realworld-parallel and
php-laravel-realworld-parallel-slo.

…ch (LANGPLAT-883)

Temporary pin until DataDog/apm-sdks-benchmarks#115 merges to main: until
then the 3 PHP yamls only exist on the leiyks/LANGPLAT-883-php-competitor-
benchmarks branch, and the parallel-benchmark-template version on main
doesn't honor DD_TRACER_ARTIFACT_DIR yet. Pointing both the include refs
and APM_SDKS_BENCHMARKS_BRANCH at the PR branch lets us validate the
end-to-end artifact-passing flow now; flip both back to 'main' once
apm-sdks-benchmarks#115 lands.

…PLAT-883)

The benchmarks.yml file is included into the child pipeline alongside
package-gen.yml (generated by generate-package.php). GitLab merges those
two files, and when both declare a top-level "stages:" block the last
one wins — our PR's stages: list was overriding package-gen's, breaking
existing jobs like "package-oci: [linux, amd64]" that target the
shared-pipeline stage.

Fix: drop the stages: block from benchmarks.yml and append the 6 PHP
stages to the single source of truth in generate-package.php. The child
pipeline now exposes the union of every stage anyone declares.

…-883)

The included .parallel-benchmark-template defines
APM_SDKS_BENCHMARKS_BRANCH="main" in its own job-level variables block,
which overrides top-level variables. Setting our PR-branch override at
the top level was a no-op — the template's job-level default still won
the merge, so the runtime clone targeted main (where tracing-libs/php/
fetch-tracing-libs.sh doesn't exist yet) and the job died with
'No such file or directory'.

Move the override into each of the 3 PHP benchmark jobs' own variables
blocks so it actually shadows the template default. Drop the top-level
variable that wasn't doing anything.