Add `Reading from a bag file (Python)` tutorial

[fujitatomoya]

Description

there are currently 3 tutorials that explains how to manage bag file,

• https://docs.ros.org/en/rolling/Tutorials/Advanced/Recording-A-Bag-From-Your-Own-Node-CPP.html
• https://docs.ros.org/en/rolling/Tutorials/Advanced/Reading-From-A-Bag-File-CPP.html
• https://docs.ros.org/en/rolling/Tutorials/Advanced/Recording-A-Bag-From-Your-Own-Node-Py.html

and we see Reading from a bag file (Python) is missing currently.

as example of rosbag2, https://github.com/ros2/rosbag2/pull/1683 added the reference example already. so we can refer to that sample to add Reading from a bag file (Python) tutorial.

Tasks

• [ ] add Reading from a bag file (Python) tutorial
• [ ] check and update already existed 3 tutorials since https://github.com/ros2/rosbag2/pull/1683 changes a bit.