Added Histograms to LOS online

[nmozumdar]

Describe your proposal.

  Added histograms to track pmt multiplicity.

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

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Checklist:

• [ ] 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