Flexibilize residues for 2nd generation bioenergy demand

[k4rst3ns]

🐦 Description of this PR 🐦

The demand for residues that is used for 2nd generation bioenergy is based on old magpie runs - 1/3 of the (back-than) sustainable fraction was used and is still enforced as exogenous demand. Due to various changes (probably also or especially also in the regional setup(?)), these demands seem to be very high, causing additional crop production of sugar cane in JPN at the moment.

We flexibilized the demand by making the exogenous demand an upper bound and adding a subsidy that enforces the removal of the residues (but no additional production of residues via additional crop production).
We take the value for the subsidy for 1st generation BE, which is already used in the model as a benchmark.

Flexibilizing can bring down the sugar cane demand in JPN:

- with the default being the current ill-behaving version. Removing the default run, it can be seen that the different subsidy levels I tested lead to slide differences at the end of the century.

Also to see how the residual removal for 2nd generation BE works the subsidy levels matter:

With subsidy at 6.5 and 10 USD17MER per GJ leading to no spiky behavior.

On the down side, costs al

so react on these new subsidies:

And run time is also much longer:

current default: 0.53 h
subsidies-6.5: 0.80 h
subsidies-10: 0.72 h

... which is coming from every time step, just needing 1 min longer to solve.

🔧 Checklist for PR creator 🔧

• Self-review own code

  • No hard coded numbers and cluster/country/region names.
  • The new code doesn't contain declared but unused parameters or variables.
  • magpie4 R library has been updated accordingly and backwards compatible where necessary.
  • scenario_config.csv has been updated accordingly (important if default.cfg has been updated)

• Document changes

  • Add changes to CHANGELOG.md
  • Where relevant, put In-code documentation comments
  • Properly address updates in interfaces in the module documentations
  • run goxygen::goxygen() and verify the modified code is properly documented

• Perform test runs

  • High risk:
    • Run test runs via Rscript start.R --> "test runs"
    • Check logs for errors/warnings
    • Default run from the PR target branch for comparison
    • Provide relevant comparison plots (land-use, emissions, food prices, land-use intensity,...)

📉 Performance changes 📈

• Current develop branch default : 0.53 h
• This PR's default : 0.80 h

🚨 Checklist for reviewer 🚨

• PR is labeled correctly
• Code changes look reasonable
  • No hard coded numbers and cluster/country/region names.
  • No unnecessary increase in module interfaces
  • model behavior/performance is satisfactory.
• Changes are properly documented
  • CHANGELOG is updated correctly
  • Updates in interfaces have been properly addressed in the module documentations
  • In-code documentation looks appropriate
• content review done (at least 1)
• RSE review done (at least 1)