fix: add pid_mode as an optional field to runner_worker_docker_options

[cmpoon]

Description

After https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/6694 was shipped in gitlab-runner 19.1.0, this adds support for defining pid_mode in the module var.

Migrations required

No, this change is backward compatible.

Verification

Added pid_mode = "host" then running a gitlab job with docker ps -q | xargs docker inspect --format '{{.State.Pid}}' in script yields the expected output indicating host pid mode.

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[Copilot]

Pull request overview

Adds support in this Terraform module for configuring Docker executor pid_mode via the existing runner_worker_docker_options variable, aligning the module with GitLab Runner >= 19.1.0’s added pid_mode support.

Changes:

• Extend runner_worker_docker_options object type to include optional pid_mode.

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