Add --start-paused option to ros2 bag play

[ivanpauno]

I think this was proposed in #443.

That PR ended up being closed in favor of #696, but an option to start the player in a paused state hasn't been added AFAIS.

[emersonknapp]

LGTM with green CI, no concerns. Thanks for the upgrade!

[ivanpauno]

This cppcheck error looks like a false positive:

Error: [rosbag2_cpp/src/rosbag2_cpp/clocks/time_controller_clock.cpp:62]: (error: selfInitialization) Member variable 'paused' is initialized by itself.

I've suppressed it in 32caf26, if another approach is prefered (e.g. renaming the argument), let me know and I will address that.

[emersonknapp]

Another option would be to name the ctor parameter bool start_paused, which should then not trigger the selfinitialization issue, right? Not going to block on that, though

[jhdcs]

This looks good to me code-wise. Only two (minor) comments on help text and variable names, but I'm not sure if we want to hold the PR back because of it.

Basically, I'm just trying to think about potential confusion points for future users and maintainers.

[ivanpauno]

CI config:

• Build: --packages-up-to rosbag2_tests ros2bag rosbag2_py rosbag2_transport
• Test: --packages-select rosbag2_tests ros2bag rosbag2_py rosbag2_transport

Jobs:

• Linux
• Linux-aarch64
• macOS
• Windows

[ivanpauno]

CI is passing, @jhdcs @emersonknapp let me know if this can be merged or if something else is missing.