Spark insert table bulk load

[anthonysena]

Fixes issues with insertTable() and bulk load with Spark (Databricks) that I introduced via #301.

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.38%. Comparing base (3766c25) to head (6187038).

Files with missing lines	Patch %	Lines
R/BulkLoad.R	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #329      +/-   ##
===========================================
- Coverage    56.40%   56.38%   -0.03%     
===========================================
  Files           16       16              
  Lines         2732     2733       +1     
===========================================
  Hits          1541     1541              
- Misses        1191     1192       +1     

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[schuemie]

@anthonysena : note that this PR is marked as a work in progress, so cannot be merged yet