Add references section to yaml schema

[rajeee]

Add a throwaway section in the yaml schema called references where yaml anchor references can be defined to be used in other places. Without this dedicated section, there is no way to define all the references at single location and one would have to define their anchor at the first point of use.

[nmerket]

Can you add a changelog entry and maybe a test that shows this working?

[github-actions]

File	Coverage
All files	84%	✅
base.py	89%	✅
eagle.py	74%	✅
exc.py	57%	✅
local.py	50%	✅
postprocessing.py	84%	✅
utils.py	96%	✅
sampler/base.py	79%	✅
sampler/downselect.py	33%	✅
sampler/precomputed.py	93%	✅
sampler/residential_quota.py	61%	✅
test/test_docker.py	33%	✅
test/test_validation.py	97%	✅
workflow_generator/base.py	90%	✅
workflow_generator/commercial.py	53%	✅
workflow_generator/residential.py	96%	✅
workflow_generator/residential_hpxml.py	69%	✅

Minimum allowed coverage is 33%

Generated by 🐒 cobertura-action against e50d9be