Add blueprint for cloud-enabled GDK

Why is this change being made?

Currently the GDK (GitLab Development Kit) allows exclusively for non-containerized local installations where developers set up and manage the full GitLab stack on their local machines with native system dependencies which leads to the following pain points:

• Reduced developer productivity due to environment troubleshooting and inconsistencies
• Increased support costs from environment-related issues and onboarding assistance
• Limited scaling capability for engineering teams and contributor base
• Environment drift causes production parity issues and unexpected bugs

This MR adds a comprehensive blueprint to propose a three-phased approach ultimately leading to a cloud-enabled architecture of GDK.

To facilitate referencing content between the top-level blueprint and the sub-blueprints this MR will contain the top-level blueprint, as well as blueprints for the first two phases.

Contributes to gitlab-org&20059 and gitlab-org/gitlab-development-kit#3117

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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Commits

• Add blueprint for cloud-native GDK

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