Tail sampling - string_attribute processor based on request header value

[bartez09]

The goal is to save tracing based on a custom requeset header:

1. saving the http request header value via opentelemetry agent:

java:
    env:
      - name: OTEL_INSTRUMENTATION_HTTP_SERVER_CAPTURE_REQUEST_HEADERS
        value: forcesampling

2. tail sampling:

    processors:      
      tail_sampling:
        decision_wait: 10s 
        num_traces: 100
        expected_new_traces_per_sec: 10
        policies:
          [   
            {
              name: test-policy,
              type: string_attribute,
              string_attribute: {key: http.request.header.forcesampling, values: [on]}
            }
          ]

Unfortunately, it seems that the key is incorrect (tracing is not saved). Please help me set it up correctly.