Timestamp split bagfiles instead of serial numbering

[emersonknapp]

Description

Name individual bagfiles with a timestamp of their start time, rather than an increasing integer index serial number.

I think most of the time, we don't care which number split a file is, but rather are interested in what time period it represents.

An illustration:

$ ros2 bag record -o my_recording --max-bag-duration 90

Should create this structure

my_recording/
├── my_recording_20250221T162100Z.mcap
├── my_recording_20250221T162230Z.mcap
├── my_recording_20250221T162400Z.mcap
└── my_recording_20250221T162530Z.mcap

Open questions:

• the format of the timestamp. Should we provide a format string option for the user to specify how they'd like their timestamps output?
• ROS Time - should the timestamps conform to simulation time when it's provided? Is that an option we even are able to enable on the recorder right now?
• Clock adjustments: if using system time, theoretically it could jump backward and potentially create the same filename twice - probably extremely unlikely but should be considered. should that be considered problem? should we allow - or force - using monotonic time?

Related Issues

Part of #1915

Discussed in #1910

Completion Criteria

_0, _1, _2 bagfile name suffixes are instead replaced with timestamps.

Implementation Notes / Suggestions

The base feature should be a relatively easy addition in the SequentialWriter, probably using std::strftime (which suggests to me that we could allow user to provide the format string without much issue).

The edge cases may end up introducing complications depending what we decide.

Testing Notes / Suggestions