frontend/node-red-dashboard: you can change the flowrate during an acquisition

[pkostyrka]

Describe the bug
During an acquisition, you can go in optic configuration and change the flowrate. It creates a bug in the software, and it should not be possible to do that.

To Reproduce
Steps to reproduce the behavior:

1. Launch an acquistion
2. Go to optic configuration
3. Change the flowrate

Expected behavior
It should not be possible to change the flowrate when an acquisition is launched.

[ethanjli]

When you change the value of the flow rate input box on the optic configuration page during acquisition, what consequences do you observe? e.g. does the pump start running at the new flow rate?

[ethanjli]

@melissadjadoun the redesign of the MQTT API should probably make the API return an error to any API client which attempts to change the flowrate while an image-acquisition sequence is running.