Draft: Add placeholder segment fit
@jojungge @syan Targets ATLASRECTS-8009
This MR adds a placeholder for segment fitting in Phase-2. This placeholder is based on a minuit2 minimizer and is not intended for production use. Rather, it serves as a placeholder to test mathematical concepts and the general segment fit strategy as well as to develop validation tools as we migrate towards the ACTS fitter. It will be use during the tracking workshop (hopefully) and replaced by the developments of that week. Also used as a basis for further development by @syan
Edited by Maximilian Emanuel Goblirsch-Kolb