Temporary fix for video latency

[amalnanavati]

Describe this pull request. Link to relevant GitHub issues, if any.

Joint PR with ada_feeding#151

Although #106 improved video streaming by replacing the dependency on web_video_server with direct subscription to compressed images, the latency of this approach depends on the device. On a desktop computer, the video stream has 1-3 sec latency, but on an iPhone 11, it has increasing latency that gets into the tens of seconds.

Looking into it, the most likely reason for this is that roslibjs uses EventEmitter2's emit event, which is synchronous. Thus, even if the subscriber on the ROS side has no queue, a queue builds up on the web app side.

The best solution to this, as documented here, is to implement WebRTC peer-to-peer streaming between the robot and web app. That is documented in issue #112 .

However, given the learning curve and time involved in implementing WebRTC, this PR and its affiliated PR ada_feeding#151 introduces a temporary fix to the problem, in the following ways:

1. Rate-limits the publication of image topics that the web app subscribes to to 3 Hz. (parameter set both in ada_feeding_perception/config/republisher.yaml and in VideoFeed.jsx)
2. Every 10 seconds, have the web app unsubscribe and re-subscribe to the topic, to clear any backlog. (parameter set in VideoFeed.jsx)

Note that these parameters can be tuned to find a subjectively optimal setting.

Explain how this pull request was tested, including but not limited to the below checkmarks.

• Pull the 2 PRs and re-build.
• Start the robot code and the web app.
• Go to bite selection, move your hand in and out of the camera, verify that the latency is not more than 1-2 secs.
• Go to the DetectingFace page, move your head around in front of the camera, verify that the latency is not more than 1-2 secs.

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