Basic Auth Added Allow Missing And Emit Dynamic Metadata

Added allow_missing field to the BasicAuth HTTP filter. When set to true, requests with no Basic credentials (missing or non-Basic Authorization header) are passed through instead of rejected, enabling OR-semantics when combining BasicAuth with other auth filters (e.g. JWT). Invalid credentials are still rejected. Added emit_dynamic_metadata field. When set to true, the filter emits dynamic metadata on successful authentication under the envoy.filters.http.basic_auth namespace with key username, allowing downstream filters (e.g. RBAC) to act on BasicAuth success.