A first look at workspaces: On-demand, cloud-based development environments

Introduced Workspaces, a new feature for on-demand, cloud-based development environments. Workspaces are ephemeral, personal development environments in the cloud, defined by code in a `.devfile.yaml` file. They require a cloud platform or self-hosted Kubernetes cluster with the GitLab Agent for Kubernetes installed. Initially, they support the Web IDE and allow for manual authentication to clone private repositories. Future plans include SSH access from desktop IDEs, support for other editors, and usage limits.