Sub-annual time step compatibility

With @behnam2015 we went through the model core and highlighted parts of code that are not yet including sub-annual time steps and this feature might be useful.

- Equations where time is missing but it is probably not necessary:
EXTRACTION_EQUIVALENCE, RESOURCE_CONSTRAINT, STOCKS_BALANCE and related
OPERATION_CONSTRAINT, MIN_UTILIZATION_CONSTRAINT

- Equations where time is missing and it would make sense to have it. However, it would lead to backwards incompatibility issues
EMISSION_EQUIVALENCE, EMISSION_CONSTRAINT
RELATION_EQUIVALENCE

- We also highlighted parts that might be incompatible or that might not be flexible to set year-to-substep mappings. For example in the commodity balance the demand can be yearly and the supply at the sub-annual time level. We are not sure if this is true for other blocks of equations and we think some others' opinion is necessary.
ADDON_ACTIVITY_LO and _UP
SHARE_CONSTRAINT_COMMODITY_UP and other share constraints
RENEWABLES_EQUIVALENCE, SYSTEM_RELIABILITY_CONSTRAINT, SYSTEM_FLEXIBILITY_CONSTRAINT and all renewable related equations

In terms of compatibility, I am not sure if `renewable_capacity_factor` should have time in it. If it is simply a multiplier at different `grades` and the variability in renewable capacity factor can be expressed in `capacity_factor`, then it should be fine.

Start by reviewing the listed equations, especially EMISSION_EQUIVALENCE, EMISSION_CONSTRAINT, RELATION_EQUIVALENCE, the addon and share constraints, and the renewable-related equations. Determine which blocks support year-to-substep mappings and where adding time would create backwards incompatibility. Done means the compatibility gaps and required design decisions are resolved across the affected equations.

Written by the indexing model from the issue text.