Update Engagement analytics logic

[lctrt]

• update engagement % counting to use members instead of total speakers
• engagement performance uses percentage data
• update engagement table to use % for performance comparison

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.45%. Comparing base (8d26292) to head (22a879a).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4426      +/-   ##
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- Coverage   99.46%   99.45%   -0.01%     
==========================================
  Files        1066     1066              
  Lines       20690    20712      +22     
  Branches     6502     6508       +6     
==========================================
+ Hits        20580    20600      +20     
- Misses        110      112       +2     

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[gabiayako]

Although it's not written down in the ticket I remember we discussed about making some adjustments to the Caption

We could take a look with Padmini how it should change though, but I think at least we agreed at the time that we would have % in the Unique Speakers All Roles and Unique Speakers: Key Personnel