Qos configurability

[ivanpauno]

Prototype of ros2/design#300.

Depends on #1410.
Diff omitting #1410: https://github.com/ros2/rclcpp/pull/1408/files/ec90cb53091e355dcf194c944fcaf239c5fa6699..9197a8f2bfe9da6e54f3e30779b3b1c0236339f2.

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Not quite ready yet.
Things to solve before merging:

1. Get the final topic name before creating a publisher/subscription

   • rcl support for expand and remap.
   • Wrap the rcl function in an rclcpp method for Node (PR).

2. create_subscription and create_publisher can be called without a parameters interface

   I'm not quite sure what to do about this.
   If the user wants to only provide a topics interface (without using qos overrides), that should be ok.
   Maybe fail when qos overrides are enabled and a parameters interface isn't provided?

   • Add create_publisher/create_subscription overload taking both a topics interface and a parameters interface (4d6ad65).
   • Handle error when qos overrides are enabled and a parameters interface isn't provided: A warning is being logged in this case.
   • See places that need special handling in rclcpp code in create_publisher.hpp/create_subscription.hpp comments.
     Added notes, this can be resolved in a follow-up.

3. Improve QosOverridingOptions API

   Not a blocker for merging this, but we should have minimal API that won't be deprecated.
   Maybe QosOverridingOptions could use the builder pattern or the parameter idiom to make things easier.
   I definitely also want either builder pattern/parameters idiom in PublisherOptions/SubscriptionOptions, but that can be done in a follow up.

4. Test coverage

   • Improve test coverage (note: this can still be improved)

5. Move things that can be shared between rclcpp/rclpy to rcl/rmw

   • Conversions between policy values and strings (PR).
   • Extend rmw_qos_policy_kind_t to cover all possible policies (and move that to a more appropriate header). Define rclcpp::QosPolicyKind values based on that. Conversions to/from strings can be implemented there (PR).
   • Use the new rmw functions in this PR (77eec6d).

6. Support in other client libraries

   • Support in rclpy (PR)