Don't require flow_type on queued flow start tasks

[rowanseymour]

It's redundant since we load the flow anyway when creating batches

[codecov-commenter]

Codecov Report

Merging #164 (c8a4ee0) into main (bc374bf) will increase coverage by 62.64%.
The diff coverage is 87.50%.

@@            Coverage Diff            @@
##           main     #164       +/-   ##
=========================================
+ Coverage      0   62.64%   +62.64%     
=========================================
  Files         0      147      +147     
  Lines         0    12302    +12302     
=========================================
+ Hits          0     7706     +7706     
- Misses        0     3761     +3761     
- Partials      0      835      +835     

Files	Coverage Δ
core/models/starts.go	44.03% <100.00%> (ø)
core/tasks/handler/contact_tasks.go	49.30% <100.00%> (ø)
core/tasks/starts/start_flow.go	69.79% <50.00%> (ø)

... and 144 files with indirect coverage changes

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