Handle 'best_available' QoS policies in common

[j-rivero]

Alternative to #84 after feedback received there.

I did not find problems on building or testing using this new approach. The PR looks cleaner.

[j-rivero]

I've added 7480115 following up the conversation in #84 (comment). That triggered some failures in the system test https://github.com/ros2/system_tests/pull/501/files

    <testcase name="test_best_available_policies_subscription" status="run" result="completed" time="0.313" timestamp="2022-04-28T16:52:18" classname="test_quality_of_service.QosRclcppTestFixture__rmw_connextdds">                         
      <failure message="/home/jrivero/code/ros2/ws_qos_adaptative/src/ros2/system_tests/test_quality_of_service/test/test_best_available.cpp:76&#x0A;Expected equality of these values:&#x0A;  actual_qos.reliability()&#x0A;    Which is: 4-b
Expected equality of these values:                                               
  actual_qos.reliability()                                                       
    Which is: 4-byte object <01-00 00-00>                                        
  publisher_qos_profile.reliability()                                            
    Which is: 4-byte object <02-00 00-00>]]></failure>                           
      <failure message="/home/jrivero/code/ros2/ws_qos_adaptative/src/ros2/system_tests/test_quality_of_service/test/test_best_available.cpp:78&#x0A;Expected equality of these values:&#x0A;  actual_qos.deadline()&#x0A;    Which is: 16-byt
Expected equality of these values:                                               
  actual_qos.deadline()                                                          
    Which is: 16-byte object <F8-34 5A-26 37-7F 00-00 FF-FF FF-FF FF-FF FF-7F>   
  publisher_qos_profile.deadline()                                               
    Which is: 16-byte object <F8-34 5A-26 37-7F 00-00 80-84 1E-00 00-00 00-00>]]></failure>
      <failure message="/home/jrivero/code/ros2/ws_qos_adaptative/src/ros2/system_tests/test_quality_of_service/test/test_best_available.cpp:80&#x0A;Expected equality of these values:&#x0A;  actual_qos.liveliness_lease_duration()&#x0A;   
Expected equality of these values:                                               
  actual_qos.liveliness_lease_duration()                                         
    Which is: 16-byte object <F8-34 5A-26 37-7F 00-00 FF-FF FF-FF FF-FF FF-7F>   
  publisher_qos_profile.liveliness_lease_duration()                              
    Which is: 16-byte object <F8-34 5A-26 37-7F 00-00 C0-C6 2D-00 00-00 00-00>]]></failure>
    </testcase>                                                                  

Am I missing a change in this PR or the changes are wrong?

[j-rivero]

One more final change to make test_quality_of_service to pass in d6f5efb.

[jacobperron]

LGTM!