Move paths defined in env vars into config model, split into server and builder config

[djeebus]

Note

Introduces BuilderConfig into orchestrator config and refactors sandbox/FC to use it; centralizes telemetry initialization with internal noop handling and unexports Otel endpoint.

• Orchestrator Config:
  • Add and embed BuilderConfig with ALLOW_SANDBOX_INTERNET, ENVD_TIMEOUT, FIRECRACKER_VERSIONS_DIR, HOST_KERNELS_DIR, ORCHESTRATOR_BASE_PATH, SANDBOX_DIR, SHARED_CHUNK_CACHE_PATH, and NetworkConfig.
  • Switch to env.ParseAs and add ParseBuilder().
• Sandbox/Firecracker:
  • Replace env var lookups with cfg.BuilderConfig across fc (paths and script builder).
  • Update fc.NewProcess and StartScriptBuilder to accept BuilderConfig.
  • sandbox.Factory now holds BuilderConfig, uses it for internet allowance and EnvdTimeout.
• Template Cache:
  • Use config.BuilderConfig.SharedChunkCachePath for shared cache.
• Telemetry:
  • Centralize client init: call telemetry.New(...) unconditionally; it now returns noop if endpoint unset.
  • Unexport OTEL_COLLECTOR_GRPC_ENDPOINT var and update exporters to use it.
• Entrypoints/Tests:
  • Adjust orchestrator, build-template cmd, and benchmarks to new config/factory signatures and imports.
  • Add tests for embedded config defaults/overrides.

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