Prep for v1.20.1

[odow]

TODO

• [Utilities] fix stackoverflow in operate(+,...) with many arguments #2285
• [Utilities] use foldl to avoid StackOverflow #2290

Basic

• version field of Project.toml has been updated
  - If a breaking change, increment the MAJOR field and reset others to 0
  - If adding new features, increment the MINOR field and reset PATCH to 0
  - If adding bug fixes or documentation changes, increment the PATCH field

Documentation

• Add a new entry to docs/src/changelog.md, following existing style

Tests

• https://github.com/jump-dev/MathOptInterface.jl/actions/runs/6267756197

[blegat]

Let's hold off until my concern in #2284 is addressed, I think we should revert #2285 as it might cause more issues by fixing an invalid use case

[blegat]

We can release, the benchmark of #2284 (comment) shows there is no regression