[CHORE] Allow multiple group_bys for pivot

[colin-ho]

Currently df.pivot only accepts a single group_by column, this PR adds functionality to use multiple columns.

[codecov]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 85.64%. Comparing base (c57aaad) to head (aeee2dc).

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #2242       +/-   ##
=========================================
+ Coverage      0   85.64%   +85.64%     
=========================================
  Files         0       71       +71     
  Lines         0     7642     +7642     
=========================================
+ Hits          0     6545     +6545     
- Misses        0     1097     +1097     

Files	Coverage Δ
daft/dataframe/dataframe.py	90.20% <100.00%> (ø)
daft/execution/execution_step.py	93.77% <100.00%> (ø)
daft/execution/rust_physical_plan_shim.py	96.25% <ø> (ø)
daft/logical/builder.py	91.04% <100.00%> (ø)
daft/table/micropartition.py	90.70% <100.00%> (ø)
daft/table/table.py	56.86% <0.00%> (ø)

... and 65 files with indirect coverage changes

[jaychia]

Nice and clean :)