[humble] Make snapshot writing into a new file each time it is triggered (backport #1842)

[mergify]

This PR will make snapshot writing into a new file each time it is triggered.

• Relates Snapshot should write to a different file every time it is triggered #1099
• This PR is a replacement for the Feature/snapshot write different file each trigger rolling #1839

Note. Snapshot now becomes a blocking call and mutually exclusive with the writer::write(message) method to avoid race conditions, i.e., blocking the same writer_mutex_.
The set_data_ready() method from #1839 is not needed since "snapshot" has now become a blocking call; therefore, there are no race conditions, and we will not dump data from the cyclic buffer twice because data_ready will be settled false after the first dump with message_cache_->notify_data_ready();.

rosbag2/rosbag2_cpp/src/rosbag2_cpp/cache/circular_message_cache.cpp

Lines 95 to 106 in 786c3c4

	void CircularMessageCache::swap_buffers()
	{
	std::lock_guard<std::mutex> producer_lock(producer_buffer_mutex_);
	// Swap buffers only if data is ready. Data not ready when we are calling flushing on exit and
	// we should not dump buffer on exit if snapshot has not been triggered.
	if (data_ready_) {
	std::lock_guard<std::mutex> consumer_lock(consumer_buffer_mutex_);
	consumer_buffer_->clear();
	std::swap(producer_buffer_, consumer_buffer_);
	data_ready_ = false;
	}
	}

However, we still need to call split_bagfile_local(true) to trigger callbacks and open a new storage file.

This PR could be backported. There are no API/ABI breaking changes in it.

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This is an automatic backport of pull request #1842 done by Mergify.