Formulas for statistics of peaks workspace

[VickieLynch]

Added latex formulas for values in statistics tables

To test:

build documentation and check for StatisticsOfPeaksWorkspace

Fixes #12651

Does not need to be in the release notes.

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[rosswhitfield]

You can link to the SortHKL algorithm here by using :ref:algm-SortHKL``

[rosswhitfield]

Looks good 👍 I didn't explicitly check the formulas but they look correct.