Migrate nginx.conf template to component

What does this merge request do and why?

This migrates the nginx.conf.erb to the new component syntax.

How to set up and validate locally

1. Run echo > nginx/conf/nginx.conf
2. Run gdk reconfigure
3. See that the file is generated again

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 MR references an issue describing the change.
• This change is backward compatible. If not, include steps to communicate to users.
• Tests added for new functionality. If not, raise an issue to follow-up.
• Observability added/updated (logging, metrics, tracing).
• Documentation added/updated.
• Announcement added for notable changes.
• gdk doctor test added.