rosdistro_build_cache: Detect GitHub rate limit throttling

[robwoolley]

When running rosdistro_build_cache as an unauthenticated user the rate limit on the REST API will cause it to fail.

The github_source_manifest_provider() function is able to detect the HTTP 403 error, however it does not understand what it means and will continue to try to access the API:

DEBUG:rosdistro:- load repo tree from https://api.github.com/repos/ros-controls/control_msgs/git/trees/foxy-devel?recursive=1
DEBUG:rosdistro:- load package.xml from https://raw.githubusercontent.com/ros-controls/control_msgs/338ef98b4a4d763fe5df39e86a1967844ceb506e/control_msgs/package.xml
  - fetch "control_msgs"
DEBUG:rosdistro:- load repo tree from https://api.github.com/repos/ros-controls/control_toolbox/git/trees/ros2-master?recursive=1
DEBUG:rosdistro:- load package.xml from https://raw.githubusercontent.com/ros-controls/control_toolbox/ae7102b7ce0c03c510adaa2d86767cf91756665e/package.xml
  - fetch "control_toolbox"
DEBUG:rosdistro:- load repo tree from https://api.github.com/repos/PickNikRobotics/cpp_polyfills/git/trees/main?recursive=1
DEBUG:rosdistro:- load package.xml from https://raw.githubusercontent.com/PickNikRobotics/cpp_polyfills/d740e5b66c14e5be1670ceca79eae1add150604a/tcb_span/package.xml
DEBUG:rosdistro:- load package.xml from https://raw.githubusercontent.com/PickNikRobotics/cpp_polyfills/d740e5b66c14e5be1670ceca79eae1add150604a/tl_expected/package.xml
  - fetch "cpp_polyfills"
DEBUG:rosdistro:Skipped "github_source_manifest_provider()": Unable to fetch JSON tree from https://api.github.com/repos/rt-net/crane_plus/git/trees/humble-devel?recursive=1: HTTP Error 403: rate limit exceeded
  - fetch "crane_plus"
DEBUG:rosdistro:Skipped "github_source_manifest_provider()": Unable to fetch JSON tree from https://api.github.com/repos/iRobotEducation/create3_sim/git/trees/main?recursive=1: HTTP Error 403: rate limit exceeded
  - fetch "create3_sim"
DEBUG:rosdistro:Skipped "github_source_manifest_provider()": Unable to fetch JSON tree from https://api.github.com/repos/AutonomyLab/create_robot/git/trees/humble?recursive=1: HTTP Error 403: rate limit exceeded
  - fetch "create_robot"
DEBUG:rosdistro:Skipped "github_source_manifest_provider()": Unable to fetch JSON tree from https://api.github.com/repos/tier4/cudnn_cmake_module/git/trees/main?recursive=1: HTTP Error 403: rate limit exceeded
  - fetch "cudnn_cmake_module"

I propose that the exception should be identified when it is caught and either cause the GitHub provider to terminate or the whole application.