Adding SunSpec storage 124 Model

[CpuID]

Whoops typo'ed model in the commit message :)

Preparation for being able to work on #68 and #8

Derived from https://github.com/sunspec/models/blob/master/json/model_124.json

[CpuID]

I thought I'd do this in multiple stages to make the review process easier.

My next goal was to handle the s/limiters/setpoints rename mentioned #68 (comment) as a separate PR, then we can start diving into what #68 starts to look like :)

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.