Suggesting transport variables and tags

[yiyi1991]

This PR proposes new transport sector tags and variables for the NGFS project (Phase VI) but also generally. Key points:

• Add new tag transport mode (Road, Rail, Active, etc.) in addition to the current vehicle-type tag (bus, truck, ldv, etc., which only sit in the subcategory of Road) and tag drive-type (BEV, ICE, etc.), so that mode shift can be presented clearly in the energy service variables.
• By default, Aviation and Shipping do not include bunkers now.
  • the previous Domestic Aviation and Domestic Shipping are not precise for activities within model regions, especially in global models
• Two-wheelers are separated from a subcategory of LDV and rescoped as 2W and 3W.

TODO

• Technical issues still remain in energy service variable namings (being able to match with how they are named in NAVIGATE, how they are defined in SDG indicators)

How to review:

• Read the files changed or generate nomenclature export-definitions . definitions.xlsx
• Do the new transport variables (especially mode-tag-related) make sense to you? (defination clear? variables exclusive?)