Skip redundant Gitaly setup in Remote development workspace

What does this merge request do and why?

Skip redundant Gitaly setup in Remote development workspace

We've already set up Gitaly during the Remote development workspace Docker image build. Skipping this redundant step at startup helps reduce the GDK's startup time.

Related to #2057

How to set up and validate locally

1. Open a new workspace.
2. Run git checkout 2057-skip-gitaly-setup.
3. Open the command palette by Ctrl + Shift + P. Then type, Reload Window.
4. The Bootstrap GDK task should start and succeed in the workspace.

After the above steps, I confirmed that starting GDK took 12 minutes and 52 seconds, compared to 19 minutes and 3 seconds previously.

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.