Switch to albumentations for augmentation

[talmo]

imgaug is woefully under-maintained and has an annoying dependency of opencv-python (instead of opencv-python-headless).

This will break in future updates, so perhaps we should consider switching to albumentations, especially since it has native keypoint support:

• https://albumentations.ai/docs/examples/example_keypoints/
• https://github.com/albumentations-team/albumentations_experimental#spatial-level-transforms

[talmo]

#1623 makes the switch, but to sort out the opencv bit, we'll need to merge in and republish the tensorflow conda packages over here since they were previously bundling opencv:

talmolab/conda_packages#1

[talmo]

Closing this one but see also:

• Replace imgaug with albumentations #1623
• Albumentations is breaking with some edge cases #1722
• Fix out of bounds albumentations issues and update dependencies #1724
• Lower bound albumentation version to handle Nan keypoints #1995