Draft a 10k scaletest plan

[spikecurtis]

Write a draft RFC which lays out the test plan for 10k scale.

• what kinds of load to generate
  • builds
  • connections
  • dashboard usage
  • proxying apps
• features to specifically test
  • prebuilds
  • notifications
  • devcontainers
  • AI Tasks
  • dynamic parameters

Plan should include 1k, 3k, and 10k targets for all load rates (e.g. requests per second).