Handle infeasability

[kvikshaug]

Adds a new status field to the return value of the simulation service which will have the value infeasible or optimal, and only in the latter case are growth and fluxes included.

Thoughts:

• We're still not using marshmallow schemas in this service, but let's do this in incremental steps
• I was considering just passing the solution.status field instead of explicitly defining "optimal" and "infeasible", but we have to do that anyway since it's inaccessible when raise_error=True.
• I think it makes sense to just keep the HTTP 200 status code since the request in itself was valid and successful, it is the business logic which is failing.
• Not sure if forcing growth bounds to (-1000, -1000) is the most intuitive way to guarantee an infeasible model, but it works...

[codecov-io]

Codecov Report

Merging #140 into devel will increase coverage by 0.6%. The diff coverage is 100%.

@@            Coverage Diff            @@
##            devel     #140     +/-   ##
=========================================
+ Coverage   71.89%   72.49%   +0.6%     
=========================================
  Files          20       20             
  Lines         804      807      +3     
=========================================
+ Hits          578      585      +7     
+ Misses        226      222      -4

Impacted Files	Coverage Δ
src/simulations/resources.py	84.21% <100%> (+0.87%)	:arrow_up:
src/simulations/modeling/simulations.py	94.44% <100%> (+10.66%)	:arrow_up:

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