RFC: Umbrella RFC for allowing GPU workloads in CF

[ZPascal]

Summary

• Adds an umbrella RFC for first-class GPU support in Cloud Foundry, covering the end-to-end path from developer manifest to device injection
• Sets shared goal, approach, and scope across affected components (BOSH/Stemcells, Diego, Garden/garden-runc, CAPI, CLI, Buildpacks, cf-deployment)

Background

CF currently has no GPU concept at any layer — Diego cannot schedule on GPU capacity, Garden cannot inject devices, and CAPI has no GPU field. This RFC establishes the umbrella design using CDI (Container Device Interface) for vendor-neutral device injection, validated by a POC on real Tesla T4 hardware.