handle enums when key passed instead of value

[gblackadder]

For pyMetadataEditor, the enums in templates can be ignored. But we don't have that option here since the enums are in the base types. So instead, make the enum robust to receiving the key as well as the value at instantiation.

For example I was seeing errors like:

series_description.related_indicators.1.type

Input should be 'concept', 'disaggregation' or 'derivation' [type=enum, input_value='Derivation', input_type=str]
For further information visit https://errors.pydantic.dev/2.10/v/enum/
I have written a custom Enum class that allows the input to be either the key or the value of the Enum.

Example:

class IndicatorType(EnumWithValueOrKey):
    Concept = "concept"
    Disaggregation = "disaggregation"
    Derivation = "derivation"
    
# Example usage:
# This will work
IndicatorType("concept")  # gives IndicatorType.Concept
IndicatorType("Concept")  # gives IndicatorType.Concept

# This will raise a ValidationError
IndicatorType("Invalid")