[FLAX] glue training example refactor
Author: kamalkraj
Pull request: yes
Labels: name: WIP

# What does this PR do?

refactor glue training example similar to other flax training examples.

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Fixes # (issue)


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Models:

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Comments:
Ping here

@patil-suraj @patrickvonplaten 
 rebased with current master

@patil-suraj - this has been open since a while now, could you please take care of it?

@patil-suraj refactored according to comments