INF-19: Add datadog + dash0 exporters + datadogconnector to OTel collector

Subtask of INF-18 (OTel-native migration). Repo: TextureHQ/kube-live, production/otel-collector/ (ArgoCD-managed, Honeycomb-only today). Add datadog exporter (DD API key, datadoghq.com intake) + dash0 OTLP exporter alongside otlp/honeycomb. Wire datadog/connector for DD APM stats. Fan out traces+metrics to HC+DD+dash0. SOPS-encrypt new secrets (DD API key + dash0 auth). Branch: havoc/inf-19-otel-dd-dash0-exporters. Blocked-ish on decision #3 (dash0 primary + does HC stay) but DD exporter+connector can proceed now regardless. Full context: projects/dash0-otel-datadog.md.