Minimum retired capacity constraint

[filippopecci]

Description

This PR introduces the option to specify a minimum capacity that should be retired by a given period. This can be used to model age based retirements for existing units.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g., docstrings for new functions, updated/new .md files in the docs folder)
• My changes generate no new warnings
• I have tested the code to ensure it works as expected
• New and existing unit tests pass locally with my changes:

julia> using Pkg
julia> Pkg.test("MacroEnergy")

• I consent to the use of the MacroEnergy.jl license for my contributions.

How to test the code

The test system is attached. One of the natural gas power plants has an existing capacity of 300 MW, 100 of which should retire by period 2 unless they are not retired earlier due to economic reasons.

test_minimum_retired_capacity.zip

Additional context

Note : the code will not run with current main because of a bug affecting multi-period planning models. The bug will be fixed by PR #135, so this PR should be merged after #135.