Workspaces Agents Admin UI: pass organization ID to Vue app

Issue: Workspaces Cluster Agents Admin Settings UI (#545241 - closed)

What does this MR do and why?

• Pass organization ID to Vue app. This will be used later on as one of the GQL query variables.
• Refactor to use Settings Block Vue component as a follow up to this feedback. This ensures that the settings body is only rendered when the settings block is expanded.
• Add missing UI requirements: add popover in Availability header and make name cells render a link that will link to the agent's web path URL once the GQL query is implemented.

References

Workspaces Cluster Agents Admin Settings UI (#545241 - closed)

Screenshots or screen recordings

demo

How to set up and validate locally

1. Go to /rails/features/ in the GDK and enable the workspaces_agents_availability_admin feature flag
2. Go to /admin/application_settings/general. Observe new setting GitLab Agents Availability. Expanding the setting reveals a table.
3. Note new UI additions: popover in the Availability column header and Name column now renders a link.

MR acceptance checklist

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