Add mAP metric for object detection

[TheCodez]

It would be a good idea to add a mAP metric which is often used in object detection. For this the newly added IoU function from torchvision could be used.

[vfdev-5]

@TheCodez yes, that's can be a good idea. If you would like to contribute, it would be 👍

[TheCodez]

@vfdev-5 I have some code here. It's probably not even working but maybe it can be used as a starting point. I don't think I can get this finished so it would be awesome if someone else could contribute here :)

[vfdev-5]

Few other implementation refs:

• https://github.com/coz-a/signate-fish-school/blob/main/src/solution/metrics.py
• https://github.com/bes-dev/mean_average_precision/