This is the continue of [#1373] discussion and related to the ros-navigation/navigation2#3325 issue in Nav2

The initial idea is to make rclcpp::Rate to work with ROS-time (currently it works only with system and steady times).

What was made:

• Add rclcpp::Clock pointer to the rclcpp::Rate constructor to allow developer to specify the clock to work with (by-default it is still RCL_SYSTEM_TIME if no clock is specified)
• Add rclcpp::ROSRate rate class, respective to ROS-time

Current implementation points:

• Getting rid of templates' structure allows developer to select the clock to work with in dynamics
• Renamed rclcpp::GenericRate -> to rclcpp::Rate and gave it the default clock to work with
• rclcpp::Rate and rclcpp::WallRate API remaining to be untouched as much as possible
• Although there are some changes in API: rclcpp::Duration instead of std::chrono::nanoseconds in durations and Rate::get_type() routine instead of previously used Rate::is_steady()
• New rclcpp::ROSRate class that working with ROS time