Make import_annotations script work against remote annotator

[MateoLostanlen]

Make import_annotations script work against remote annotator with token refresh and TLS flag

Body

• Read annotation API credentials from ANNOTATOR_LOGIN and ANNOTATOR_PASSWORD environment variables with CLI overrides
• Add robust token management with automatic refresh on HTTP 401 for list and patch operations
• Add --verify-ssl flag to control TLS validation when calling the annotation API
• Keep existing behaviour of merging old labels into new annotations while preserving bounding boxes
• Manually tested against https://annotationdev.pyronear.org/api/v1 with a real backup file and the new environment variables