apply_classification should allow cusomisation of label values

[atmorling]

In a case such as classifying continuous values into discrete bins, it would be helpful to allow a user to specify how the label values are formatted, without needing to know the exact ranges of bins as created by apply_classify

[atmorling]

This will be most useful in a workflows context when generating things like the speedmap
xref - https://github.com/wildlife-dynamics/ecoscope-workflows/issues/280