build(frontend): Optimize Docker build time and image size

[Pwuts]

The AutoGPT Platform frontend image is currently 5.3GB and takes forever to build and cache.

This PR reduces image size by 4.9GB (93%) and reduces uncached build time from ~7m to ~5m20s.

Changes 🏗️

• Use cache mount to prevent Yarn cache from being included in yarn install layer
• Leverage Next.js output tracing to generate minimal application w/ tree-shaken dependencies
• Add non-root user following the reference Dockerfile

Checklist 📋

For code changes:

• I have clearly listed my changes in the PR description
• I have made a test plan
• I have tested my changes according to the test plan:
  • ...

Example test plan

• Create from scratch and execute an agent with at least 3 blocks
• Import an agent from file upload, and confirm it executes correctly
• Upload agent to marketplace
• Import an agent from marketplace and confirm it executes correctly
• Edit an agent from monitor, and confirm it executes correctly

[netlify]

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