[SYSTEMDS-3830] Add join operator to Scuro

[christinadionysio]

This patch adds a new join operator to scuro. The join operation takes two modalities as well as a join condition as input and joins the two modalities on their common dimension (temporal for now). This includes two new modalities and the ability to apply new representations on top of a joined modality. In the future the join operator will also serve as a simple alignment operator by joining two modalities by a given offset.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.38%. Comparing base (5ff6274) to head (81342aa).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2220      +/-   ##
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- Coverage     72.38%   72.38%   -0.01%     
- Complexity    45381    45384       +3     
============================================
  Files          1468     1468              
  Lines        170802   170802              
  Branches      33306    33306              
============================================
- Hits         123634   123628       -6     
- Misses        37762    37767       +5     
- Partials       9406     9407       +1     

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