Change name of repository to `model_seg_lesion_mp2rage`

[jcohenadad]

To be consistent with the sister repository: https://github.com/ivadomed/model_seg_sc_mp2rage

[uzaymacar]

Closing this issue as discussed in the previous meeting (i.e. no need to change the name of repository) because

• we decided to have a single repository for both models and
• the lesion and sc separation is therefore no longer necessary: we can stick to ms.