## Why
Managed OpenTelemetry requirements could not specify span attributes or tracestate metadata.
## What changed
- Accept `otel.span_attributes` and `otel.tracestate` in requirements, merge them by attribute or member field, and expose them through app-server configuration and requirements reads.
- Protect required entries and their ancestors from configuration writes while preserving unmanaged sibling values and their origins. For example, requiring `otel.tracestate.vendor.tenant` leaves `vendor.region` writable. Empty metadata maps impose no requirements.
- Select Rustls when configuring an OTLP HTTP client certificate and private key so PEM client identities are accepted.
## Testing
Add coverage for metadata precedence, effective configuration, field-level write protection, and preservation of unmanaged values. Add blocking and asynchronous HTTP client construction tests using generated PEM certificates and keys.
GitOrigin-RevId: ada6000cc5e575b9a33451ec4aa58b6686dc20f7
Abhinav
154e8736a5