REF: split describe categorical function

[ivanovmg]

• xref REF: NDFrame describe #36833
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

Moved handing timestamp data from describe_categorical_1d into describe_timestamp_as_categorical_1d.
Extracted function select_describe_func for selecting the proper function, suitable for a given data type.

Pros:

• Simplified logic on which function is selected for which data type.
• Improved way of issuing FutureWarning.
• Next logical step in enabling the strategy pattern.

Cons:

• Unnecessary argument percentiles_ignored passed into functions for handling categorical types. This is done to unify the interface across all functions for describing a series. The problem will be handled when enabling strategy pattern as the percentiles will become an instance attribute for the strategy class.
• Slight duplication in describe_categorical_1d into describe_timestamp_as_categorical_1d, which will be handled as the strategy class for categorical data is created (it will be encapsulated there).