Allow adding attributes at any step
Created by: fbudin69500
Currently, it is technically possible to define a new attribute after step 0, but that attribute is not saved if the first step has been performed.
It would be important to either:
- Let the user know that the attribute is not saved, both in ADIOS2 documentation and maybe with an error message (throw).
- Save (new) attributes at each step.
This is especially true for attributes for transient variables that are not known before a certain step.