Single SSP repository

[DagBruck]

We now have two SSP respositories:

• https://github.com/modelica/ssp-standard
• https://github.com/modelica/ssp-standard-dev

I find this super-confusing, we should standardize (!) on one of them and move what ever issues etc. from the old one. And finally close the old one (make it read-only).

[beutlich]

It's at least somehow in line with FMI and DCP, see https://github.com/modelica/MA-Internal?tab=readme-ov-file#project-resources. It even would fit better if https://github.com/modelica/ssp-standard-dev could be renamed to https://github.com/modelica/ssp-design.

[pmai]

Moving most stuff over to the ssp-standard is the plan, however the time to do this is was deemed to be after the 2.0 release, since this allows a clean break and does not cause confusion on feature planning.