Implement validation for routing-only

[JordanLaserGit]

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For your point on pointing the sloth bmi model to a fake forcing file, I'm fine with this. Instead of troute.yaml, we could set it to /dev/null and have the validation skip checking the forcing file if the path is /dev/null. Your hack could work as well, just probably makes more sense to point to /dev/null than a file that potentially could not exist. Ideally SKIP_VALIDATION is not a required arg for a routing-only run, but perhaps this is out of scope for this PR. I'll make an issue so we can deal with this later.
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Originally posted by @JordanLaserGit in #51 (comment)

[quinnylee]

Initializing formulations
/usr/include/c++/11/bits/stl_vector.h:1045: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = std::vector<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::vector<std::__cxx11::basic_string<char> > >; std::vector<_Tp, _Alloc>::reference = std::vector<std::__cxx11::basic_string<char> >&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__n < this->size()' failed.

I think setting the forcing path to /dev/null breaks sloth? The new code is in the routing-only-val branch, commit hash 274cb7c and the command used to run it is

rm -rf /home/ec2-user/outputs && docker pull awiciroh/datastream:routing-only-val &&
docker pull awiciroh/forcingprocessor:latest &&
export DS_TAG=routing-only-val FP_TAG=latest && /home/ec2-user/datastreamcli/scripts/datastream -s DAILY -n 4 --FORCING_SOURCE NWM_V3_CHRTOUT_SHORT_RANGE_00 -d /home/ec2-user/outputs -r s3://ciroh-community-ngen-datastream/v2.2_resources/VPU_03W -R /home/ec2-user/datastreamcli/configs/ngen/realization_sloth_troute.json --S3_BUCKET ciroh-community-ngen-datastream-test --S3_PREFIX outputs/routing_only/v2.2_hydrofabric/ngen.DAILY/short_range/00/VPU_03W

[quinnylee]

I've reverted back to making config/troute.yaml the dummy forcings file since it will always exist for a routing only run. run_validator.py still checks to see if that's the forcings file, and if it is, it will skip catchment validation. See latest comits in routing-only-val