LAMB Optimizer - rename weight_decay_rate to weight_decay

[ksachdeva]

Describe the bug

Unlike the rest of the optimizers API, in LAMB the name of the argument for weight_decay is weight_decay_rate

In my experiments where I try various different optimizers, this makes me add a special condition for LAMB because of this different name of the argument.

Code to reproduce the issue

addons/tensorflow_addons/optimizers/lamb.py

Line 44 in 8cec33f

weight_decay_rate: FloatTensorLike = 0.0,

[bhack]

I think that you can introduce a deprecation and add the new argument name with a PR.
You can handle the deprecation like in #2048

[ksachdeva]

Thanks. I will send the pull request.