feat: add preemptive_mode option passthrough on docker_autoscaler

[maxvandermeij]

Description

Allow passthrough of the preemptive_mode value on the runner_worker_docker_autoscaler_autoscaling_options as described on the doc that is linked on the code https://docs.gitlab.com/runner/configuration/advanced-configuration/#the-runnersautoscalerpolicy-sections

Should resolve the error on the message logs

gitlab-runner: jsonschema: '/runners/0/Autoscaler/Policy/0/PreemptiveMode' does not validate with https://gitlab.com/gitlab-org/gitlab-runner/common/config#/$ref/properties/runners/items/$ref/properties/Autoscaler/$ref/properties/Policy/items/$ref/properties/PreemptiveMode/type: expected boolean, but got null

Migrations required

No migrations required

Verification

Ive confirmed this by adding the preemptive_mode value on the runner_worker_docker_autoscaler_autoscaling_options properties and confirmed by enabled the "debug_write_runner_config_to_file = true" to see it being added on the runners autoscaler policy

#module 
runner_worker_docker_autoscaler_autoscaling_options = [
  {
    periods      = ["* 7-19 * * mon-fri"]
    timezone     = "Europe/Amsterdam"
    idle_count   = 0
    idle_time    = "30m"
    scale_factor = 5
    preemptive_mode = true
  }

#toml
[[runners.autoscaler.policy]]
  idle_count = 0
  idle_time = "30m"
  periods = ["* 7-19 * * mon-fri"]
  **preemptive_mode = true**
  scale_factor = 5
  scale_factor_limit = 0
  timezone = "Europe/Amsterdam"

[github-actions]

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[maxvandermeij]

Did not yet figure out which of the values is the current default, if you find out do let me know. My guess is "false" but need to do some more testing

[kayman-mk]

See https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/5565

It depends on idle_count.

[maxvandermeij]

See https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/5565

It depends on idle_count.

So true as a default. Edit: actually not setting a default makes more sense as it will allow users to choose the behaviour type that they want. Automatic based on idle_count or specifically set based on this parameter.