Address hardcoded 2018 MECS in GHG methods

[catherinebirney]

cc:
Closes: #488

What changed? Why?

• Address the hard coded use of 2018 MECS data when we want generic code so we can either use 2018 or 2022 in the GHG FBS methods
• Addressed by moving away from the EIA_MECS_Energy_CEDA_allocaition.yaml FBA and instead created FBS methods
• Moving to FBS also allows us to use the Cornerstone_2015 industry spec and move away from the hard coded EIA_GHGI tables used in the ceda approach - important now that the methods use UMD_GHGIA data

Testing