GKE Upgrade Agent: Extend to App Developer Analysis

[bryk]

Goal
Implement the next phase of the GKE Upgrades Agent, focusing on supporting Application Developers (workload owners) in preparing their codebases for upcoming GKE version upgrades.

Core Customer User Journey (CUJ)
Codebase-Specific Upgrade Report for App Developers

The agent will provide a specialized report focusing solely on changes required within an application's codebase to maintain compatibility with the new GKE version.

As an App Developer (workload owner), I need a concise report from the GKE Upgrades Agent that tells me exactly what changes I need to make in my application's code and configurations (e.g., deployment manifests) to handle an upcoming GKE upgrade.

Scope
Focus: Changes required inside the workload codebase (e.g., deprecated APIs, changes in Kubernetes client libraries, or specific application configurations affected by the new GKE/Kubernetes version).
Input: Access to the workload codebase (assumed to be available to the developer/agent).
Output: A report that isolates the necessary code and configuration updates for the individual workload.

Success Criteria
The agent successfully identifies and reports on breaking changes within a sample application's code against a target GKE version.
Positive feedback from workload owners regarding the clarity and utility of the codebase-specific report.

[bryk]

Open discussion whether we want to target "against a target GKE version" and/or general best practices