Fix lr scheduler to update before creating the checkpoint

[rohitgr7]

What does this PR do?

Fixes #4655

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[rohitgr7]

The only problem left here is with ReduceLROnPlateau. This scheduler needs a monitor to update. If it's done on epoch level then it won't get the monitored key/value since checkpoints are created before epoch metrics are aggregated. Does anyone got a suggestion??

[rohitgr7]

fixing it here: #5208