Log LearningRateMonitor values to Trainer.callback_metrics for EarlyStopping

[baskrahmer]

…ntegration with EarlyStopping

What does this PR do?

Logs the LearningRateMonitor values to Trainer.callback_metrics such that this is natively accessible by the EarlyStoppingCallback when conditioning on a specific LR key.

Fixes #17449

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[awaelchli]

Great addition!
If you could add a comment in the src/lightning/pytorch/CHANGELOG.md as well, that would be great!