Increase MlflowLogger parameter value length limit

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### Description & Motivation

Currently, MlflowLogger parameter value length is limited to 250 (#5893) which is too low for class names, data augmentations or others.
Recent MLflow support up to 6000 (mlflow/mlflow#9709).

### Pitch

MLflow use `mlflow.utils.validation.MAX_PARAM_VAL_LENGTH` to validate parameter value length.
`mlflow.utils.validation.MAX_PARAM_VAL_LENGTH` exist in mlflow >= 1.0
I believe we can use it to reliably truncate parameter value without checking MLflow version.

```python
class MLFlowLogger(Logger):
@rank_zero_only
def log_hyperparams(self, params: Union[Dict[str, Any], Namespace]) -> None: # type: ignore[override]
...
from mlflow.utils.validation import MAX_PARAM_VAL_LENGTH
# Truncate parameter values to MAX_PARAM_VAL_LENGTH characters.
params_list = [Param(key=k, value=str(v)[:MAX_PARAM_VAL_LENGTH]) for k, v in params.items()]
...
```

### Alternatives

_No response_

### Additional context

_No response_

cc @lantiga @borda

Start at MLFlowLogger.log_hyperparams and review how parameter values are currently truncated to 250 characters. Check MLflow's MAX_PARAM_VAL_LENGTH behavior, then verify that logged parameter values are truncated to that limit without breaking existing logging behavior.

Written by the indexing model from the issue text.