Resolve "Include AI Gateway in GDK"

What does this merge request do and why?

This MR adds support for installing, updating and running the GitLab AI Gateway, using the steps documented at https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/blob/main/README.md#how-to-run-the-server-locally.

cc @dsatcher, @andr3, @oregand

How to set up and validate locally

1. Check out this branch, 2025-include-ai-gateway-in-gdk-2
2. Stop your GDK
3. Run gdk config set gitlab_ai_gateway.enabled true
4. Run make Procfile gitlab-ai-gateway-setup, ensuring your watch the output and verify your Google Cloud login
5. You can also run make gitlab-ai-gateway-update as well to ensure this works
6. Now run either gdk start gitlab-ai-gateway or just gdk start
7. You can watch the status of the service by running gdk tail gitlab-ai-gateway
8. Once you see something along the lines of "Application startup complete." in the gdk tail gitlab-ai-gateway` output, you should be able to hit http://localhost:5052/docs and see the AI Gateway running
9. Also confirm that running gdk status prints => GitLab AI Gateway is available at http://localhost:5052. at the bottom of its output.

You could also create a new GDK instance using the 2025-include-ai-gateway-in-gdk-2 branch with the same steps to ensure everything works from scratch:

1. cd /tmp
2. git clone git@gitlab.com:gitlab-org/gitlab-development-kit.git
3. cd gitlab-development-kit
4. git checkout 2025-include-ai-gateway-in-gdk-2
5. make bootstrap
6. gdk config set gitlab_ai_gateway.enabled true
7. make install
8. Verify using the same steps earlier

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.

Closes #2025 (closed)