Improve opentelemetry tracing
    
    - Make sure all (buffered) spans are processed.
    
    - Use span of API call as parent of backend spans
    
    ```
    odcs-client: odcs-client
        odcs-client: POST
            odcs: /api/1/composes/
                odcs: generate-compose
    ```
    
    Previously, `generate-compose` span is at the same level as
    `/api/1/composes/` span.
    
    JIRA: RHELCMP-11789