Add Test::Integration::AiGateway Scenario

What does this MR do and why?

Relates to https://gitlab.com/gitlab-org/quality/quality-engineering/team-tasks/-/issues/2128

This MR adds a new AiGateway component and Test::Integration::AiGateway scenario in order to help test the code suggestions cloud licensing and authentication workflows for self-managed GitLab instances.

Related GitLab MR: gitlab!139717 (merged)

Test pipeline with specs: https://gitlab.com/gitlab-org/gitlab-qa/-/pipelines/1107551985

• Please see the ai-gateway-sync-seat-link and ai-gateway-sync-service-token jobs for results

Next Steps 👉

• Open an MR for GitLab to update the following (done: gitlab!139717 (merged))
  • Update qa/specs/features/ee/api/14_model_ops/code_suggestions_spec.rb to run against this orchestrated scenario
  • Add a new AiGateway scenario class to qa/ee/scenario/test/integration
  • Update main.gitlab-ci.yml to include two new jobs that will run this scenario with and without the QA_USE_SYNC_SERVICE_TOKEN_WORKER environment variable. This will allow us to run tests against both the SyncServiceTokenWorker and SyncSeatLinkWorker workflows when generating a code suggestions access token, which is currently controlled by the feature flag <code data-sourcepos="22:473-22:501">use_sync_service_token_worker</code>.
• After that, work on the next iteration of updating qa/specs/features/ee/browser_ui/3_create/web_ide/code_suggestions_in_web_ide_spec.rb to also run in this orchestrated scenario

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Check out this branch and add the following env vars:

export GITLAB_LICENSE_MODE=test
export QA_EE_ACTIVATION_CODE=<found in 1Password>

Optionally, you can also include QA_USE_SYNC_SERVICE_TOKEN_WORKER to also test the SyncServiceTokenWorker flow:

export QA_USE_SYNC_SERVICE_TOKEN_WORKER=true

2. Run the following command locally to spin up the containers with no tests:

exe/gitlab-qa Test::Integration::AiGateway EE --no-tests

4. Once the containers are up a running, login to the GitLab instance as the admin user and create a new personal access token.
5. Send a cURL request to the code_suggestions/completions endpoint, such as the one below:

curl --location 'http://<gitlab_docker_url>/api/v4/code_suggestions/completions' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer <admin_token>' \
--data '
  {
    "prompt_version": 1,
    "current_file": {
      "file_name": "main.py",
      "content_above_cursor": "def reverse_string(s):\n    return s[::-1]\ndef test_empty_input_string()",
      "content_below_cursor": ""
    }
  }'

6. Verify that the request is successful and that you receive a response

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.