Traces(otlp): Wire OTLP span naming and validation settings

[webern]

Background

ADP must carry otlp_config.traces.span_name_as_resource_name and otlp_config.traces.span_name_remappings into resolved OTLP trace configuration and reject configurations with no enabled OTLP signal. Naming consumption belongs to otlp_v1_naming_kill_switches; these settings have no consumer until that work lands.

Agent behavior

pkg/trace/config/config.go:59-71 defines SpanNameRemappings and SpanNameAsResourceName for OTLP ingest. comp/otelcol/otlp/config.go:85-87 returns at least one OTLP signal needs to be enabled when metrics, traces, and logs are disabled. The ingest path does not validate remap keys, values, or ignore_resources regexes.

ADP behavior

domains::otlp::Traces in lib/agent-data-plane-config exposes enabled, internal_port, probabilistic_sampler_sampling_percentage, string_interner_size, enable_compute_top_level_by_span_kind, and ignore_missing_datadog_fields, but neither span-name field. ADP has no at-least-one-signal check.

Configuration keys

• otlp_config.traces.span_name_as_resource_name
• otlp_config.traces.span_name_remappings

Acceptance

• Resolved OTLP trace configuration contains span_name_as_resource_name
• Resolved OTLP trace configuration contains span_name_remappings
• Startup fails when OTLP metrics, traces, and logs are all disabled