Expand definitions and documentation about pre/post-input/output operations

[fmigneault]

🚀 Feature Request

For an input, value_scaling, resize_type and pre_processing_function can be used.
However, it is ambiguous what should happen (how to interpret the MLM) if all are combined simultaneously.

• Should this be disallowed?
• Should the specific order to apply them predefined (needing custom pre_processing_function otherwise)

Furthermore, the output allows a similar post_processing_function.
Although the text does describe normalization/resize operations in a similar fashion, there is no concept of value_scaling and resize_type in that case.

• Should those be added to the output?
• Is there anything else missing that could be needed?

🔉 Motivation

Refine/unify definitions.

📡 Alternatives

n/a

📎 Additional context

• Relates to refactor norm-type/statistics mlm:input properties #39