2D correlation plot of tpat in R3BGeneralOnlineSpectra

[ryotani]

A 2D plot to illustrate tpat values in each event is added. This will be useful to monitor the Trloii functions for Foot-on and Foot-bonus triggers.

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Mention any issue this PR is resolved or is related to.

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Checklist:

• [X] Rebased against dev branch
• [X] My name is in the resp. CONTRIBUTORS/AUTHORS file
• [X] Followed the pull request guidlines and the Git workflow
• [X] Followed the seven rules of great commit messages

[ryotani]