Learning rate schedule is now a config class

[hyenal]

To avoid to over parametrise the learning rate schedule class I propose to make them serializable objects. This is also related to https://github.com/martinsbruveris/tensorflow-image-models/discussions/38

[martinsbruveris]

One comment about code style: please run make style followed by make quality on your code.

• make style applies black formatting and import sorting
• make quality checks black formatting, import sorting and also runs flake8

[martinsbruveris]

Another small suggestion: rename lr_schedules.py to simply schedules.py. To keep names short.

Looking good! Thanks for the PR.

[hyenal]

Thanks :) It now pass the test but I still have to modify the examples to modify the schedule there :)

[martinsbruveris]

Looks good! Will merge once unit tests pass.