add confg for engaging

[yueyanglu]

Major changes

• Types.jl: Added optfile to MITgcm_config so users can specify their own optional file
• ModelSteps.jl: Updated config.inputs[:setup][:build][:options] to include optfile in the genmake2 process
• ShellScripting.jl: Modified create_script to allow user-specified script templates
• ... :Added script_for_engaging for MIT Engaging job submission

P.S.
To build and run, users have to load proper environments in or before starting Julia. Here is an example in Julia (specific to Engaging):

MITgcm.setenv("DATADEPS_ALWAYS_ACCEPT", true) 
ENV["PATH"] = "/orcd/software/core/001/spack/pkg/openmpi/4.1.4/zahpnmk/bin:" * ENV["PATH"]
ENV["CC"] = "mpicc" 
ENV["FC"] = "mpifort" 
ENV["F90C"] = "mpifort" 
MITgcm.setenv("MPI_INC_DIR", "/orcd/software/core/001/spack/pkg/openmpi/4.1.4/zahpnmk/include")
MITgcm.setenv("NETCDF_ROOT", "/orcd/software/community/001/spack/pkg/netcdf-fortran/4.6.1/gxllmsl") 
run(`which mpicc`) 
run(`which mpifort`)