Make crashdumps optional in config

[Porges]

Make crashdumps optional in task definition so that old CLI clients are not rejected.

[codecov-commenter]

Codecov Report

Merging #3409 (d65a141) into main (9420f51) will decrease coverage by 0.02%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #3409      +/-   ##
==========================================
- Coverage   34.20%   34.18%   -0.02%     
==========================================
  Files         297      297              
  Lines       36406    36423      +17     
==========================================
  Hits        12452    12452              
- Misses      23954    23971      +17     

Files Changed	Coverage Δ
src/ApiService/ApiService/onefuzzlib/Defs.cs	0.00% <0.00%> (ø)
src/agent/onefuzz-task/src/local/libfuzzer_fuzz.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-task/src/local/template.rs	6.35% <0.00%> (ø)
...nt/onefuzz-task/src/tasks/fuzz/libfuzzer/common.rs	17.28% <0.00%> (-0.35%)	:arrow_down:
...rc/agent/onefuzz-task/src/tasks/fuzz/supervisor.rs	0.00% <0.00%> (ø)

[Porges]

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