Add DCP startup OTEL tracing

[davidfowl]

Description

Adds startup OTEL tracing support for DCP and centralizes startup profiling instrumentation in internal/telemetry.

• Adds DCP startup context propagation from Aspire via environment variables and resource annotations.
• Configures DCP OTEL export so startup spans can correlate with Aspire CLI and Hosting profiling traces.
• Adds startup spans for DCP command execution, API server startup, controller startup, resource reconciliation, executable/container/service management, and extension discovery.
• Centralizes DCP startup span names, event names, and attribute names behind telemetry constants and a StartupSpan wrapper so call sites do not expose raw span details.

Validation

• go test ./internal/telemetry ./internal/dcp/commands ./internal/dcp/bootstrap ./internal/dcpctrl/commands ./controllers ./cmd/dcp
• go test ./... was attempted locally; it fails on existing local test prerequisites/environment issues such as missing .toolbin/delay.

Notes

This pairs with the Aspire startup OTEL harness work so exported traces can validate correlated CLI, Hosting, and DCP startup spans.