Update energy service variables & Add Useful Energy

[jkikstra]

For ScenarioMIP analysis, per discussion in #270 and also discussion with @vruijven @christophbertram @gunnar-pik @volker-krey

[jkikstra]

Not sure what exactly is causing the 'illegal character' error:

=========================== short test summary info ============================
FAILED tests/test_legacy.py::test_legacy_variables - ValueError: Collected 2 errors:
  1. Unexpected character in variable: 'Production|Iron and Steel'. Check for illegal characters and/or if tags were spelled correctly.
  2. Unexpected character in variable: 'Production|Non-Metallic Minerals'. Check for illegal characters and/or if tags were spelled correctly.
FAILED tests/test_reserved_terms.py::test_variable_ops_as_square_brackets - ValueError: Collected 2 errors:
  1. Unexpected character in variable: 'Production|Iron and Steel'. Check for illegal characters and/or if tags were spelled correctly.
  2. Unexpected character in variable: 'Production|Non-Metallic Minerals'. Check for illegal characters and/or if tags were spelled correctly.
========================= 2 failed, 1 warning in 6.05s =========================

[jkikstra]

OK thanks @vruijven for your thoughts. Now updated. Would be great if we can move this in such that we can use it for JUSTMIP submissions.

[jkikstra]

@phackstock @danielhuppmann can we go ahead here, or is there any additional changes needed?

Note: we could also delete Useful Energy [per capita] variables from the sdg YAML