Add Env(params::Dict) for setting parameters before GRBstartenv

[odow]

Closes #588

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.

Project coverage is 92.40%. Comparing base (2e84ecd) to head (e2558c4).

Files with missing lines	Patch %	Lines
src/MOI_wrapper/MOI_wrapper.jl	66.66%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #596      +/-   ##
==========================================
+ Coverage   92.21%   92.40%   +0.18%     
==========================================
  Files           6        6              
  Lines        2658     2658              
==========================================
+ Hits         2451     2456       +5     
+ Misses        207      202       -5     

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