Add workspaces in gdk.yml

Issue: GDK: Add workspaces in gdk.yml (#2261 - closed)

What does this merge request do and why?

Introduce Workspaces in gdk.yml .

How to set up and validate locally

1. Setup dnsmasq for pointing workspaces.gdk.test and its subdomains to the listen_address (e.g. 172.16.123.1). There is a separate issue to make this part of GDK itself - GDK: Introduce dnsmasq service (#2694)

   # Reference - https://allanphilipbarku.medium.com/setup-automatic-local-domains-with-dnsmasq-on-macos-ventura-b4cd460d8cb3
   
   ## Step 1: Install and configure Dnsmasq
   
   brew install dnsmasq
   
   mkdir -pv $(brew --prefix)/etc/
   
   echo 'address=/workspaces.gdk.test/172.16.123.1' >> $(brew --prefix)/etc/dnsmasq.conf
   
   sudo brew services start dnsmasq
   
   dig x.workspaces.gdk.test @127.0.0.1
   
   ## Step 2: Create a dns resolver and test setup
   
   sudo mkdir -v /etc/resolver
   
   sudo bash -c 'echo "nameserver 127.0.0.1" > /etc/resolver/workspaces.gdk.test'
   
   sudo killall -HUP mDNSResponder
   
   ## Step 3: Verify
   
   dig x.workspaces.gdk.test

2. Checkout GitLab on vtak/agentw_integration_test branch.
3. Generate certs for workspaces domain in your GDK directory - mkcert "*.workspaces.gdk.test"
4. Modify gdk.yml

   ---
   gitlab_k8s_agent:
     agent_listen_address: gdk.test:8150
     enabled: true
     k8s_api_listen_address: gdk.test:8154
   hostname: gdk.test
   listen_address: 172.16.123.1
   nginx:
     enabled: true
     http:
       enabled: true
   workspaces:
     enabled: true

5. gdk reconfigure.
6. gdk restart
7. Browse https://does-not-exist-yet.workspaces.gdk.test:3555/ and verify the response is Not found.

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, 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.
  • Once this is merged, documentation will be added in https://gitlab.com/gitlab-org/workspaces/gitlab-workspaces-docs/-/blob/main/doc/local-development-environment-setup.md?ref_type=heads .
• Announcement added, if change is notable.
• gdk doctor test added, if needed.