Allow create workspace form to be prefilled

To improve user experience when creating workspaces from merge requests, we want to allow the frontend form to be automatically prefilled using URL parameters. This should enable faster, workspace launches directly when coming from MR reviews. We also want to allow prefilling of environment variables.

Current State

Even though the form appears prefilled in most cases, for the Devfile and Cluser Agent fields, we simply select the first one in the list on the UI. We also don't allow prefilling of environment variables.

Proposal

• Update the frontend form to accept and apply values from URL parameters.
• Ideally, the entire form can be completed, enabling one-click workspace launches.
• Ensure values passed via URL are validated and sanitized.