Improve Geti workflows directory layout

[leoll2]

Goal: remove ambiguous references to geti/otx domain in Geti folders, while keeping a separation between the 'job' and 'trainer' parts of the training job, which map to different Docker images.

Proposed layout

workflows/
├─ dataset_ie/
├─ optimize/
├─ train/
│  ├─ job/
│  ├─ trainer/
│  │  ├─ xpu/
│  │  ├─ gpu/
│  │  ├─ scripts/

Notes:

• the folders 'geti_domain' and 'otx_domain' are removed
• the trainer scripts and images for gpu/xpu, previously in 'otx_domain/trainer/otx_v2', are now moved under the 'train/' folder
• the optimization job also depends on the 'trainer'; this is not an issue because it just needs the Docker image, regardless of the folders layout in the source code