[jsk_fetch_startup] Add image hertz converter for recording kitchen demo

[tkmtnt7000]

This pull request addresses the issue of the incorrect correspondence between audio and video in the recording video of kitchen demo.
Specifically in this change, the previous image topic is continued to publish until the next image topic is published to be a specific frequency.

• before (audio and video not syncronized): https://drive.google.com/uc?id=1z4PNl8J-YN436_ncONAtY3mn7nP-CtBa
• after (syncronized better): https://drive.google.com/uc?id=1H1P82VCIQxVoxVj58Vei70mx7OZXL07F

I'm also thinking a little that it might be better to move image_hz_converter.py to something like jsk_topic_tools not only for sensor_msgs/Image but also for more general topics.

[knorth55]

@tkmtnt7000 it would be better to add this node to jsk_topic_tools, I think.
The difference between topic_tools/throttle is that this node keep the hz in stable, right?
I think for another topics, you can use AnyMsg and get_message_class.
https://github.com/jsk-ros-pkg/jsk_common/blob/30cdff0624b253d58af2b00ccdf0277cf27d9ec1/jsk_tools/src/delay_timestamp.py

[tkmtnt7000]

Thank you for advice.
I'll move this node to jsk_topic_tools for another topics.

[knorth55]

@tkmtnt7000 これってマージしていいんだっけ？

[tkmtnt7000]

jsk_topic_toolsに出しているknorth55/jsk_common#3
jsk-ros-pkg/jsk_common#1719
に対応させた形で出し直します..

[tkmtnt7000]

Move to #205