Simplify `gdk update` and `gdk reconfigure` by removing duplicate logic

What does this merge request do and why?

This MR removes redundant logic in gdk update and gdk reconfigure commands, and introduces a new check-duplicates command.

The make update command updates all necessary services running in GDK, while make reconfigure only enables or disables specific features like gitlab-docs or elasticsearch when gdk.yml is modified.

To avoid duplication, services running by default are removed from make reconfigure. All necessary services are started by the make update command.

Closes #1639 (closed)

How to set up and validate locally

mkdir ~/tmp
cd ~/tmp && git clone git@gitlab.com:gitlab-org/gitlab-development-kit.git
cd gitlab-development-kit && git checkout 1639-remove-duplicate-logic-in-gdk-update
make bootstrap
make install
make update

If you want to check for any duplicated lines between make update and make reconfigure, you can run:

make check-duplicates command="(make update && make reconfigure)"

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.