[ITS] add payload size plot to FEE task + minor improvements

[pfecchio]

No description provided.

[iravasen]

@pfecchio please set nBins in the TH2 (y axis) in the json so that we can easily change it without going with another PR. Thank you!

[iravasen]

Thank you @pfecchio
@Barthelemy for us this PR can be merged.

[iravasen]

My comment arrived too early. Anyway I confirm it can be merged for us. Thank you

[Barthelemy]

@TimoWilken @ktf The status of the checks have been "waiting to be reported" since yesterday. Could you have a look ?

[knopers8]

@pfecchio Is a first time contributor, but I clicked the github button to allow the checks to run. Perhaps our CI does not respond to this?

[TimoWilken]

Hi @Barthelemy, @knopers8, you're right, our CI doesn't respond to this. The checks will run if you approve the PR using the GitHub review functionality.

[iravasen]

@Barthelemy @knopers8 can this be merged? Unfortunately from the logs I cannot see if the issue with o2-cs8 is related to "arrow" as usual.