adding support for scenario based quantity targets

[Renato-Rodrigues]

Purpose of this PR

• Add support for scenario based quantity targets
• Previously quantity targets were only defined directly in the scenario config file by using switch cm_implicitQttyTarget. This limited direct documentation in the code of the values used for quantity targets, and the complexity and number of quantity targets applied to any given scenario due to the GAMS 255 characters line limits.
• This PR adds support for defining scenarios that represent specific quantity targets and use keyword to enable them in any given scenario.
• You can find more detail about how to use this feature in the main.gms switch documentation.

Type of change

• New feature

Checklist:

• My code follows the coding etiquette
• I performed a self-review of my own code
• I explained my changes within the PR, particularly in hard-to-understand areas
• All automated model tests pass (FAIL 0 in the output of make test)

Further information (optional):

• Test runs are here:
  /p/projects/ecemf/REMIND/2040_scenarios/v08_2024_06_14_REMIND_3.3.1/output

[robertpietzcker]

ok